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# Programming-Idioms.org

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Pascal
1
Print a literal string on standard output
``WriteLn('Hello, world!');``
2
Loop to execute some code a constant number of times
``````var
i: integer;
begin
for i:=1 to 10 do
WriteLn('Hello');
end;``````
3
Like a function which doesn't return any value, thus has only side effects (e.g. Print to standard output)
``````Procedure finish(name: String);
Begin
WriteLn('My job here is done. Goodbye ', name);
End;``````
4
Create a function which returns the square of an integer
``````Function square(x: Integer): Integer;
Begin
Result := x*x;
End;``````
5
Declare a container type for two floating-point numbers x and y
``````Type
TPoint = Record
x : Double;
y : Double;
End;``````
6
Do something with each item x of the list (or array) items, regardless indexes.
``for x in items do ;``
7
Print each index i with its value x from an array-like collection items
``````var I:Integer;
Items: array of String;
[..]
for I := 0 to high(Items) do
WriteLn('Item ', I, ' = ', Items[I]);
``````
Alternative implementation:
``````var I:Integer;
Items: array of TObject;
[...]
for I := 0 to high(Items) do
if assigned(Items[I]) then
WriteLn(Format('Item %d = %s', [I, Items[I].ToString]));
``````
8
Create a new map object x, and provide some (key, value) pairs as initial content.
``````type TMap = specialize TFPGMap<String, Integer>;
var x: TMap;

begin
x := TMap.Create;
x['one'] := 1;
x['two'] := 2;
end.
``````
9
The structure must be recursive because left child and right child are binary trees too. A node has access to children nodes, but not to its parent.
``````type
generic BinTree<T> = class
Value: T;
Left, Right: BinTree;
end;   ``````
10
Generate a random permutation of the elements of list x
``````var Iter,rr: integer;
[...]
for Iter := 0 to high(x) do
begin
rr := random(high(x))+1;
tmp := x[Iter];
x[Iter] := x[rr];
x[rr] := tmp;
end;``````
11
The list x must be non-empty.
``````element := x[random(length(x))];
``````
Alternative implementation:
``element := x.Items[random(x.count)];``
12
Check if the list contains the value x.
list is an iterable finite container.
``````result := false;
for e in list do
if e=x then
begin
result := true;
break;
end
``````
Alternative implementation:
``result := list.IndexOf(x) <> -1;``
Alternative implementation:
``````p := list;
while (p <> nil) and (p^.key = x) do p := p^.next;
found := p.key = x``````
13
Access each key k with its value x from an associative array mymap, and print them.
``````for i := 1 to mymap.Count 		do
WriteLn(mymap.Keys[i], '=', mymap.Data[i]);``````
14
Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.
``````function pick(a, b:real): real;
begin
result := a + random * (b - a);
end;
``````
15
Pick a random integer greater than or equals to a, inferior or equals to b. Precondition : a < b.
``````var
_a, _b, _r: Integer;
begin
_r := RandomRange(_a, _b);
end; ``````
17
The structure must be recursive. A node may have zero or more children. A node has access to its children nodes, but not to its parent.
``````type
TTree = class
Children: array of TTree;
Data: TObject;
end;     ``````
Alternative implementation:
``````type
generic
TTree<_T> = class(TObject)
Children: array of TObject;
Data: _T;
end;

type
TStringTree = specialize TTree<String>;
``````
19
Reverse the order of the elements of the list x.
This may reverse "in-place" and destroy the original ordering.
``````var n,i: integer;
[...]
n:= length(x);
setlength(x, n+1);
for i := 0 to (n div 2)-1 do
begin
x[n] := x[i];
x[i] := x[n-i-1];
x[n-i-1] := x[n];
end;
setlength(x, n);``````
Alternative implementation:
``````var n,i: integer;
tmp:TElement;
[...]
n:= length(x);
for i := 0 to (n div 2)-1 do
begin
tmp := x[i];
x[i] := x[n-i-1];
x[n-i-1] := tmp;
end;``````
20
Implement a function search which looks for item x in a 2D matrix m.
Return indices i, j of the matching cell.
Think of the most idiomatic way in the language to return the two values at the same time.
``````procedure search(m:T2dMatrix; x:TElement; out i,j:integer);
begin
for i := 0 to high(m) do
for j := 0 to high(m[i]) do
if m[i,j] = x then
exit;
i := -1;
j := -1;
end;``````
21
Swap the values of the variables a and b
``````tmp := a;
a := b;
b := tmp;``````
22
Extract the integer value i from its string representation s (in radix 10)
``i := StrToInt(S);``
23
Given a real number x, create its string representation s with 2 decimal digits following the dot.
``s := format('%.2f',[ x]);``
24
Declare a new string s and initialize it with the literal value "ネコ" (which means "cat" in japanese)
``````{\$codepage utf8}
s := "ネコ";``````
25
Share the string value "Alan" with an existing running process which will then display "Hello, Alan"
``````var Queue: TIdThreadSafeStringList;

type

procedure Execute; override;
end;

begin
while not Terminated do begin
Sleep(10);
with Queue.Lock do try
while Count > 0 do begin
WriteLn('Hello, ', Strings[0]);
Delete(0);
end;
finally
Queue.Unlock;
end;
end;
end;

begin
Sleep(5000);
end.
``````
26
Declare and initialize a matrix x having m rows and n columns, containing real numbers.
``var _x: array[_m,_n] of Double;``
27
Declare and initialize a 3D array x, having dimensions boundaries m, n, p, and containing real numbers.
``var x: array [m,n,p] of double;``
28
Sort the elements of the list (or array-like collection) items in ascending order of x.p, where p is a field of the type Item of the objects in items.
``````type

TItem = class p: Integer; end;
TItems = specialize TFPGObjectList<TItem>;

var items: TItems;

function compare(const a, b: TItem): Integer;
begin
Result := a.p - b.p;
end;

begin
items := TItems.Create;
items.Sort(@compare);
end.  ``````
29
Remove i-th item from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
Note that in most languages, the smallest valid value for i is 0.
``````list[i] := list[high(list)];
setlength(list,high(list));``````
30
Launch the concurrent execution of procedure f with parameter i from 1 to 1000.
Tasks are independent and f(i) doesn't return any value.
Tasks need not run all at the same time, so you may use a pool.
``````type

i: Integer;
constructor Create(const _i: Integer);
procedure Execute; override;
end;

begin
i := _i;
FreeOnTerminate := True;
inherited Create(False);
end;

begin
f(i);
end;

var i: Integer;

begin
for i := 1 to 1000 do begin TThreadF.Create(i);
end.  ``````
31
Create the recursive function f which returns the factorial of the non-negative integer i, calculated from f(i-1)
``````type
TPositiveInt = 0..MaxInt;

function _f(_i: TPositiveInt): Integer;
begin
if (_i < 2) then
Result := 1
else
Result := _f(_i - 1);
end; ``````
32
Create function exp which calculates (fast) the value x power n.
x and n are non-negative integers.
``````function exp(x: integer; n: integer): integer;

begin
if n = 0 then
Result := 1
else if n = 1 then
Result := x
else if (n and 1) = 0 then
Result := exp(x * x, n div 2)
else
Result := x * exp(x * x, n div 2);
end;``````
Alternative implementation:
``````function exp(x: QWord; n: integer): QWord;

begin
if n = 0 then
Result := 1
else if n = 1 then
Result := x
else if (n and 1) = 0 then
Result := exp(x * x, n div 2)
else
Result := x * exp(x * x, n div 2);
end;``````
33
Assign to the variable x the new value f(x), making sure that no other thread may modify x between the read and the write.
``````var
loc: TCriticalSection;
begin
loc.Enter;
try
x := f(x);
finally
loc.Leave;
end;
end.``````
38
Find substring t consisting in characters i (included) to j (excluded) of string s.
Character indices start at 0 unless specified otherwise.
Make sure that multibyte characters are properly handled.
``t := copy(s,i+1,j-i);``
Alternative implementation:
``t := s.Substring(i,j-i);``
39
Set the boolean ok to true if the string word is contained in string s as a substring, or to false otherwise.
``ok := pos(word,s)<>0;``
41
Create the string t containing the same characters as the string s, in reverse order.
The original string s must remain unaltered. Each character must be handled correctly regardless its number of bytes in memory.
``````Function ReverseString(const AText: string): string;
var
i,j:longint;
begin
setlength(result,length(atext));
i:=1; j:=length(atext);
while (i<=j) do
begin
result[i]:=atext[j-i+1];
inc(i);
end;
end;``````
Alternative implementation:
``````function reverse(const str: string): string;
var
i, j: Integer;
begin
j := length(str);
setlength(reverse, j);
for i := 1 to j do
reverse[i] := str[j - i + 1];
end;``````
42
Print each item v of list a which is not contained in list b.
For this, write an outer loop to iterate on a and an inner loop to iterate on b.
``````  for v in a do
begin
for  w in b do
if (v = w) then
break;
if (v = w) then
Continue;
writeln(v);
end;              ``````
43
Look for a negative value v in 2D integer matrix m. Print it and stop searching.
``````var i,j: integer;
flag:boolean;
[...]
for i := 0 to length(m) * length(m[0]) - 1 do
begin
v := m[i mod length(m), i div length(m)];
if v < 0 then
begin
writeln(v);
break;
end;
end;

for i := 0 to high(m) do
begin
for v in m[i] do
begin
flag := (v < 0);
if flag then
begin
writeln(v);
break;
end;
end;
if flag then
break;
end;
``````
44
Insert the element x at position i in the list s. Further elements must be shifted to the right.
``s.Insert(i, x)``
45
Sleep for 5 seconds in current thread, before proceeding with the next instructions.
``sleep(5000);``
46
Create the string t consisting of the 5 first characters of the string s.
Make sure that multibyte characters are properly handled.
``_t := Copy(_s, 1, 5);``
47
Create string t consisting in the 5 last characters of string s.
Make sure that multibyte characters are properly handled.
``````Function RightStr(const AText: AnsiString; const ACount: Integer): AnsiString;
var j,l:integer;
begin
l:=length(atext);
j:=ACount;
if j>l then j:=l;
Result:=Copy(AText,l-j+1,j);
end;
``````
48
Assign to variable s a string literal consisting in several lines of text, including newlines.
``````var
_s: String;
begin
_s := 'one' + LineEnding + 'two' + LineEnding + 'three'
end.``````
Alternative implementation:
``````var
s: String;
begin
s := 'one' + sLineBreak + 'two' + sLineBreak + 'three'
end.``````
Alternative implementation:
``````var
s: String;
begin
s := '''
one
two
three
''';
end.``````
49
Build list chunks consisting in substrings of the string s, separated by one or more space characters.
``````chunks.StrictDelimiter := True;
chunks.Delimiter := ' ';
chunks.DelimitedText := s;``````
50
Write a loop that has no end clause.
``While True do { nothing };``
Alternative implementation:
``repeat until false;``
51
Determine whether the map m contains an entry for the key k
``m.IndexOf(k) >= 0``
52
Determine whether the map m contains an entry with the value v, for some key.
``m.IndexOfData(v) >= 0``
53
Concatenate elements of string list x joined by the separator ", " to create a single string y.
``````var
_x: Array of string;
_y: String;
i: Integer;
begin
_y := ''; //initialize result to an empy string
// assume _x is initialized to contain some values
for i := Low(_x) to High(_x) do
begin
_y := _y + _x[i];
if i < High(_x) then _y := _y + ';';
end;
end;``````
54
Calculate the sum s of the integer list or array x.
``````var
_x: Array of integer;
_s, i: Integer;
begin
_s := 0;
//assume _x contains some values
for i := Low(_x) to High(_x) do _s := _s + _x[i];
end;``````
55
Create the string representation s (in radix 10) of the integer value i.
``````var
_s: String;
_i: Integer;
begin
_s := IntToStr(_i);
end.``````
Alternative implementation:
``Str(i,s);``
57
Create the list y containing the items from the list x that satisfy the predicate p. Respect the original ordering. Don't modify x in-place.
``````function Filter(vv:integer):boolean;

begin
result :=  vv mod 2= 0;
end;

type TFilter=function(v:integer):boolean;

function FilteredArray(const x:TBoundArray;p:TFilter):TBoundArray;
var
Idx: Integer;
v : Integer;

begin
setlength(result,high(x)+1);
Idx := 0;
for v in x do
if p(v) then
begin
result[Idx] := v;
inc(Idx);
end;
setlength(result,Idx);
end;
[...]
y := FilteredArray(x,@Filter);
``````
58
Create the string lines from the content of the file with filename f.
``````var
_lines, _f: String;
SL: TStringList;
begin
SL := TStringList.Create;
_lines := SL.Text;
SL.Free;
end;``````
59
Print the message "x is negative" to standard error (stderr), with integer x value substitution (e.g. "-2 is negative").
``writeln(StdErr, Format('%d is negative',[-2]));``
Alternative implementation:
``writeln(StdErr , x , ' is negative');``
60
Assign to x the string value of the first command line parameter, after the program name.
``````var
_x: String;
begin
_x := ParamString(1);
end.``````
61
Assign to the variable d the current date/time value, in the most standard type.
``````var
_d: TDateTime;
begin
_d := Now;
end.``````
62
Set i to the first position of string y inside string x, if exists.

Specify if i should be regarded as a character index or as a byte index.

Explain the behavior when y is not contained in x.
``i := Pos(y, x);``
63
Assign to x2 the value of string x with all occurrences of y replaced by z.
Assume occurrences of y are not overlapping.
``````x2 := StringReplace(x, y, z, [rfReplaceAll]);
``````
64
Assign to x the value 3^247
``````var
X: TValue;
begin
X := Exp(3, 247);
end.``````
65
From the real value x in [0,1], create its percentage string representation s with one digit after decimal point. E.g. 0.15625 -> "15.6%"
``s :=format('%.1f%%', [100.0*x]);  ``
67
Calculate binom(n, k) = n! / (k! * (n-k)!). Use an integer type able to handle huge numbers.
``````var
N, K, Res: TValue;
begin
Res := BinomN(N, K);
end.``````
68
Create an object x to store n bits (n being potentially large).
``````procedure task;
var
x: TBits;
n: integer;
begin
n := \$FFF;
x := TBits.Create(n);
end;``````
Alternative implementation:
``````procedure Task;
var
x: Set Of Byte;
begin
x:= [2,4,8,16,32,64,256];
end;``````
69
Use seed s to initialize a random generator.

If s is constant, the generator output will be the same each time the program runs. If s is based on the current value of the system clock, the generator output will be different each time.
``````var
SomeInteger: Integer;
Value: double;
begin
...
//initializes the PRNG's seed with a value depensing on system time
Randomize;
Value := random;
...
//Output will be the same eacht time the program runs
RandSeed := SomeInteger;
Value := random;
...
end.``````
70
Get the current datetime and provide it as a seed to a random generator. The generator sequence will be different at each run.
``Randomize;``
71
Basic implementation of the Echo program: Print all arguments except the program name, separated by space, followed by newline.
The idiom demonstrates how to skip the first argument if necessary, concatenate arguments as strings, append newline and print it to stdout.
``````PROGRAM Echo;

VAR
I: Integer;
BEGIN
for I := 1 to ParamCount - 1 do
Write(ParamStr(I), ' ');
if (ParamCount > 0) then
Write(ParamStr(ParamCount));
WriteLn();
END.``````
73
Create a factory named fact for any sub class of Parent and taking exactly one string str as constructor parameter.
``````type Parent = class
constructor create(const str: string);
end;

type ClassOfParent = class of Parent;

function fact(ClassType: ClassOfParent; const str: string): Parent;
begin
result := ClassType.Create(str);
end;``````
74
Compute the greatest common divisor x of big integers a and b. Use an integer type able to handle huge numbers.
``````function GCD(a,b:int64):int64;

var t:int64;

begin
while b <> 0 do
begin
t := b;
b := a mod b;
a := t;
end;
result := a;
end;
``````
76
Create the string s of integer x written in base 2.

E.g. 13 -> "1101"
``````var Iter,n:integer;
[...]
S := '';
for Iter := 0 to n do
s:= Char(Ord('0')+(x shr Iter) and 1) + S;   ``````
Alternative implementation:
``````var
_x: Integer;
_s: String;
begin
_s := IntToBin(_x,8*SizeOf(Integer));
end.``````
77
Declare a complex x and initialize it with value (3i - 2). Then multiply it by i.
``````var
C: Complex;
begin
C := 3*i - 2;
end.``````
78
Execute a block once, then execute it again as long as boolean condition c is true.
``````repeat
Something;
SomethingElse;
until
c;``````
Alternative implementation:
``````repeat
Something;
SomethingElse;
until not c;``````
79
Declare the floating point number y and initialize it with the value of the integer x .
``````var
y: single;
begin
y := x;
end;``````
80
Declare integer y and initialize it with the value of floating point number x . Ignore non-integer digits of x .
Make sure to truncate towards zero: a negative x must yield the closest greater integer (not lesser).
``````var
y: integer;
x: single = -0.8;
begin
y := trunc(x);
end;``````
81
Declare the integer y and initialize it with the rounded value of the floating point number x .
Ties (when the fractional part of x is exactly .5) must be rounded up (to positive infinity).
``````var
y: integer;
x: double;
begin
y := round(x);
end.``````
82
Find how many times string s contains substring t.
Specify if overlapping occurrences are counted.
``````function Count(t, s: String): Integer;
var
Offset, P: Integer;
begin
Result := 0;
Offset := 1;
P := PosEx(t, s, Offset);
while P > 0 do
begin
Inc(Result);
P := PosEx(t, s, P + 1);
end;
end;``````
83
Declare regular expression r matching the strings "http", "htttp", "httttp", etc.
``````with TRegExpr.Create('htt+p') do try
finally
free;
end;``````
84
Count number c of 1s in the integer i in base 2.

E.g. i=6 → c=2
``````function BitCount(N: Int64): Integer;
var
Q: QWord;
i: Integer;
begin
Result := 0;
Q := QWord(N);
for i := 0 to (8 * SizeOf(N) - 1) do
begin
if ((Q and 1) = 1) then Inc(Result);
Q := Q shr 1;
end;
end;``````
Alternative implementation:
``c := PopCnt(i);``
85
Write boolean function addingWillOverflow which takes two integers x, y and return true if (x+y) overflows.

An overflow may be above the max positive value, or below the min negative value.
``````function AddingWillOverFlow(x,y: Integer): Boolean;
begin
Result := (x > 0) and (y > 0) and (x > (MaxInt-y));
end;``````
Alternative implementation:
``````function AddingWillOverFlow(x,y: Integer): Boolean;
begin
Result := ((x > 0) and (y > 0) and (x > (High(Integer)-y))) or
((x < 0) and (y < 0) and ((Low(Integer)-x) > y));
end;``````
86
Write the boolean function multiplyWillOverflow which takes two integers x, y and returns true if (x*y) overflows.

An overflow may reach above the max positive value, or below the min negative value.
``````function MultiplyWillOverflow(x, y: Integer): Boolean;
begin
if ((x and y) = 0) then
Result := False
else
begin
if ((x > 0) and (y > 0)) or ((x < 0) and (y < 0)) then
Result := ((High(Integer) div Abs(x)) > Abs(y))
else
Result := Abs(Low(Integer) div Abs(x)) > Abs(y);
end;
end; ``````
87
Exit immediately.
If some extra cleanup work is executed by the program runtime (not by the OS itself), describe it.
``halt(0);``
88
Create a new bytes buffer buf of size 1,000,000.
``````var
buf: Pointer;
begin
buf := GetMem(1000000);
end;    ``````
89
You've detected that the integer value of argument x passed to the current function is invalid. Write the idiomatic way to abort the function execution and signal the problem.
``Raise EInvalidArgument.CreatFmt('Invalid value: %d',[x]);``
90
Expose a read-only integer x to the outside world while being writable inside a structure or a class Foo.
``````type Foo = class
private fx: integer;
public property x: integer read fx;
end;``````
92
Write the contents of the object x into the file data.json.
``````var
str: TMemoryStream;
jss: string;
begin
with TJSONStreamer.Create(nil) do try
str := TMemoryStream.Create;
try
jss := ObjectToJSONString(x);
str.Write(jss[1], length(jss));
str.SaveToFile('data.json');
finally
str.Free;
end;
finally
Free;
end;
end.``````
93
Implement the procedure control which receives one parameter f, and runs f.
``````procedure control(f: tprocedure);
begin
if Assigned(f) then f;
end; ``````
95
Assign to variable x the length (number of bytes) of the local file at path.
``x := filesize(path);``
96
Set the boolean b to true if string s starts with prefix prefix, false otherwise.
``b := pos(prefix, s) = 1;``
97
Set boolean b to true if string s ends with string suffix, false otherwise.
``b := AnsiEndsStr(suffix, s);``
98
Convert a timestamp ts (number of seconds in epoch-time) to a date with time d. E.g. 0 -> 1970-01-01 00:00:00
``````var
D: TDateTime;
TS: TTimeStamp;
begin
D := TimeStampToDateTime(TS);
end.``````
99
Assign to the string x the value of the fields (year, month, day) of the date d, in format YYYY-MM-DD.
``````DefaultFormatSettings.ShortDateFormat := 'yyyy-mm-dd';
X := DateToStr(D);``````
100
Sort elements of array-like collection items, using a comparator c.
``````with TList.Create do try
Sort(c);
finally
Free;
end;``````
101
Make an HTTP request with method GET to the URL u, then store the body of the response in the string s.
``````with TFPHTTPClient.Create(nil) do try
s := get(u);
finally
Free;
end;``````
102
Make an HTTP request with method GET to the URL u, then store the body of the response in the file result.txt. Try to save the data as it arrives if possible, without having all its content in memory at once.
``````var
str: TMemorystream;
begin
with TFPHTTPClient.create(nil) do
try
str := TMemoryStream.create;
try
get(u, str);
str.saveToFile('result.txt');
finally
str.free;
end;
finally
free;
end;
end;``````
105
Assign to the string s the name of the currently executing program (but not its full path).
``s := ExtractFileName(ParamStr(0));``
106
Assign to string dir the path of the working directory.
(This is not necessarily the folder containing the executable itself)
``dir := expandfilename('.');``
107
Assign to string dir the path of the folder containing the currently running executable.
(This is not necessarily the working directory, though.)
``dir := extractfilepath(paramstr(0));``
Alternative implementation:
``dir := GetCurrentDir;``
108
Print the value of variable x, but only if x has been declared in this program.
This makes sense in some languages, not all of them. (Null values are not the point, rather the very existence of the variable.)
``````{\$if DECLARED(x)}
writeln(x);
{\$endif}``````
109
Set n to the number of bytes of a variable t (of type T).
``n := SizeOf(T);``
110
Set the boolean blank to true if the string s is empty, or null, or contains only whitespace ; false otherwise.
``blank := trim(s) = '';``
111
From current process, run program x with command-line parameters "a", "b".
``````var
p: tprocess;
begin
p.Executable := 'program_x';
p.Execute;
end.``````
115
Set boolean b to true if date d1 is strictly before date d2 ; false otherwise.
``b := (CompareDateTime(d1,d2) = -1);``
116
Remove all occurrences of string w from string s1, and store the result in s2.
``s2 := stringreplace(s1, w, '', [rfReplaceAll]);``
Alternative implementation:
``s2 := s1.Replace(w,'');``
Alternative implementation:
``s2 := s1.Replace(w,''.Empty);``
117
Set n to the number of elements of the list x.
``n := length(x);``
118
Create the set y from the list x.
x may contain duplicates. y is unordered and has no repeated values.
``for i := Low(X) to High(X) do Include(Y,X[i]);``
119
Remove duplicates from the list x.
Explain if the original order is preserved.
``````var
x: TList;
begin
for i:= x.count-1 downto 0 do
if x.indexOf(x.items[i]) <> -1 then
x.delete(i);
end;``````
120
Read an integer value from the standard input into the variable n
``read(n);``
122
Create an enumerated type Suit with 4 possible values SPADES, HEARTS, DIAMONDS, CLUBS.
``````Type
Suit = (Spades, Hearts, Diamonds, Clubs);``````
123
Verify that predicate isConsistent returns true, otherwise report assertion violation.
Explain if the assertion is executed even in production environment or not.
``````{\$ASSERTIONS ON}
Assert(isConsistent,'isConsistent assertion failed.');``````
124
Write the function binarySearch which returns the index of an element having the value x in the sorted array a, or -1 if no such element exists.
``````function BinarySearch(X: Integer; A: Array of Integer): Integer;
var
L, R, I, Cur, answer: Integer;
isIt :boolean;
begin
isIt := false;
if Length(A) = 0 then Exit;
L := Low(A);
R := High(A);
while ((L <= R) AND (isIt = false)) do
begin
I := L + ((R - L) div 2);
Cur := A[I];
if (X = Cur) then begin
isIt := true;
end;
if (X > Cur) then
L := I + 1
else
R := I - 1
end;
end;``````
Alternative implementation:
``````function binarySearch (x: integer; a: array of integer): integer;
var  L, R, M: integer;  // left, right, middle
begin
if Length(a)=0 then Exit(-1);
L := Low (a);
R := High(a);
while (L <= R) do begin
M := (L + R) div 2;
if (x = a[M]) then Exit(M);  // found x in a
if (x > a[M])
then L := Succ(M)
else R := Pred(M);
end;
end;``````
125
measure the duration t, in nanoseconds, of a call to the function foo. Print this duration.
``````var
t1, t: QWord;
begin
t1 := GetTickCount64;
foo;
t := (GetTickCount64 - t1) * 1000000;
writeln(t);
end.``````
126
Write a function foo that returns a string and a boolean value.
``````type
TFooRec = record
S: String;
B: Boolean;
end;

function Foo: TFooRec;
begin
Result.S := 'Some string';
Result.B := False;
end;``````
127
Import the source code for the function foo body from a file "foobody.txt".
``````procedure foo;
begin
{\$I foobody.txt}
end;``````
131
Execute f1 if condition c1 is true, or else f2 if condition c2 is true, or else f3 if condition c3 is true.
Don't evaluate a condition when a previous condition was true.
``if c1 then f1 else if c2 then f2 else if c3 then f3;``
132
Run the procedure f, and return the duration of the execution of f.
``````var
Start, Duration: DWord;  // replaces TDateTime
begin
Start := GetTickCount64;  // better than Now
f;
Duration := GetTickCount64 - Start;
end.``````
133
Set boolean ok to true if string word is contained in string s as a substring, even if the case doesn't match, or to false otherwise.
``OK := Pos(LowerCase(AWord), LowerCase(S)) > 0;``
134
Declare and initialize a new list items, containing 3 elements a, b, c.
``````var
Items: TList;
a,b,c: pointer;
begin
Items := TList.Create;
end.``````
135
Remove at most 1 item from list items, having the value x.
This will alter the original list or return a new list, depending on which is more idiomatic.
If there are several occurrences of x in items, remove only one of them. If x is absent, keep items unchanged.
``````i := items.IndexOf(x);
if i <> -1 then
items.delete(i);``````
136
Remove all occurrences of the value x from list items.
This will alter the original list or return a new list, depending on which is more idiomatic.
``````var
i: integer;

for i:= items.count-1 downto 0 do
if items[i] = x then
items.delete(i);``````
137
Set the boolean b to true if the string s contains only characters in the range '0'..'9', false otherwise.
``````var
S: String;
C: Char;
B: Boolean;

for C in S do
begin
B := C in ['0'..'9'];
if not B then Break;
end;
``````
138
Create a new temporary file on the filesystem.
``````var
H: THandle;
begin
H := FileCreate(GetTempFileName);
end.
``````
139
Create a new temporary folder on filesystem, for writing.
``````var
GUID: TGUID;
Succes: Boolean;

begin
CreateGUID(GUID);
Succes := CreateDir(GetTempDir + GUIDToString(GUID));
end.``````
140
Delete from map m the entry having key k.

Explain what happens if k is not an existing key in m.
``m.delete(k);``
141
Iterate in sequence over the elements of the list items1 then items2. For each iteration print the element.
``````for i := 0 to items1.Count-1 do writeln(items1[i]);
for i := 0 to items2.Count-1 do writeln(items2[i]);``````
142
Assign to string s the hexadecimal representation (base 16) of integer x.

E.g. 999 -> "3e7"
``s := IntToHex(x);``
Alternative implementation:
``S := Format("%x", [x]);``
143
Iterate alternatively over the elements of the lists items1 and items2. For each iteration, print the element.

Explain what happens if items1 and items2 have different size.
``````for i := 0 to Min(items1.Count-1,items2.Count-1) do
writeln(items1[i],', ',items2[i]);``````
144
Set boolean b to true if file at path fp exists on filesystem; false otherwise.

Beware that you should never do this and then in the next instruction assume the result is still valid, this is a race condition on any multitasking OS.
``b := FileExists(fp);``
145
Print message msg, prepended by current date and time.

Explain what behavior is idiomatic: to stdout or stderr, and what the date format is.
``writeln(DateToStr(Now), #32, msg);``
146
Extract floating point value f from its string representation s
``f := StrToFloat(s);``
Alternative implementation:
``f := s.ToExtended;``
147
Create string t from string s, keeping only ASCII characters
``````var
i: integer;
begin
t := '';
for i := 1 to length(s) do
if s[i] < #128 then t := t + s[i];
end.``````
Alternative implementation:
``````var
s,t: string;
begin
t := ReplaceRegExpr('[^\u0000-\u007F]+', s, '', False);
end.``````
148
Read a list of integer numbers from the standard input, until EOF.
``````type
TFloatList = specialize TFPGList<Double>;
var
List: TFloatList;
D: Double;

begin
List := TFloatList.Create;
while not Eof do
begin
end;
List.Free;
end.``````
149
As an exception, this content is not under license CC BY-SA 3.0 like the rest of this website.
`` ``
150
Remove the last character from the string p, if this character is a forward slash /
``````begin
AllowDirectorySeparators := AllowDirectorySeparators + ['/'];
p := ExcludeTrailingPathDelimiter(p);
end;``````
Alternative implementation:
``````var
Len: Integer;
begin
Len := Length(p);
if (Len > 0) and (p[Len] = '/') then Delete(P, Len, 1);
end;``````
151
Remove last character from string p, if this character is the file path separator of current platform.

Note that this also transforms unix root path "/" into the empty string!
``````begin
p := ExcludeTrailingPathDelimiter(p);
end.``````
Alternative implementation:
``````begin
p := ChompPathDelim(p);
end.``````
152
Create string s containing only the character c.
``````var
s: string;
begin
s := 'c';
end.``````
153
Create the string t as the concatenation of the string s and the integer i.
``t := s + IntToStr(i);``
Alternative implementation:
``t := s + i.ToString;``
154
Find color c, the average between colors c1, c2.

c, c1, c2 are strings of hex color codes: 7 chars, beginning with a number sign # .
Assume linear computations, ignore gamma corrections.
``````var
c1, c2: string;
RGB1, RGB2: LongInt;
R1, G1, B1, R2, G2, B2: Byte;
c: TColor;
begin
RGB1 := ColorToRGB(StrToInt(StringReplace(c1,'#','\$',[])));
RGB1 := ColorToRGB(StrToInt(StringReplace(c2,'#','\$',[])));
RedGreenBlue(RGB1, R1, G1, B1);
RedGreenBlue(RGB2, R2, G2, B2);
c := RGBToColor(R1+R2 div 2, G1+G2 div 2, B1+B2 div 2);
end.``````
155
Delete from filesystem the file having path filepath.
``````begin
if DeleteFile(filepath) then
writeln(filepath,' succesfully deleted.')
else
writeln('Error deleting ',filepath);
end.``````
156
Assign to the string s the value of the integer i in 3 decimal digits. Pad with zeros if i < 100. Keep all digits if i1000.
``s := format('%.3d',[i]);``
157
Initialize a constant planet with string value "Earth".
``````const
planet = 'Earth';``````
158
Create a new list y from randomly picking exactly k elements from list x.

It is assumed that x has at least k elements.
Each element must have same probability to be picked.
Each element from x must be picked at most once.
Explain if the original ordering is preserved or not.
``````function RandArr(Max: Integer): TIntegerDynArray;
var
i, j, temp: Integer;
begin
SetLength(Result, Max+1);
for i := Low(Result) to High(Result) do Result[i] := i;
i := Length(Result);
while i > 0 do
begin
Dec(i);
j := RandomRange(0,i);
temp := Result[i];
Result[i] := Result[j];
Result[j] := temp;
end;
end;

var
Idx: TIntegerDynArray;
begin
Idx := RandArr(High(X));
SetLength(Y, k);
for i := 0 to k-1 do Y[i] := X[Idx];
end.``````
160
Execute f32() if platform is 32-bit, or f64() if platform is 64-bit.
This can be either a compile-time condition (depending on target) or a runtime detection.
``````begin
{\$ifdef cpu64}
f64;
{\$endif}
{\$ifdef cpu32}
f32;
{\$endif}
end.``````
161
Multiply all the elements of the list elements by a constant c
``````for i := Low(elements) to High(elements) do
elements[i] := elements[i] * c;``````
162
execute bat if b is a program option and fox if f is a program option.
``````function HasOption(c: char): Boolean;
var
i: integer;
begin
Result := False;
for i := 1 to ParamCount do
if (ParamStr(i) = ('-' + c)) then Exit(True);
end;

begin
if HasOption('b') then Bat;
if HasOption('f') then Fox;
end.``````
163
Print all the list elements, two by two, assuming list length is even.
``````i := Low(L);
while (i < High(L)) do
begin
writeln(L[i],', ', L[i+1]);
Inc(i,2);
end;``````
164
Open the URL s in the default browser.
Set the boolean b to indicate whether the operation was successful.
``b := OpenUrl(s);``
165
Assign to the variable x the last element of the list items.
``x := items[high(items)];``
166
Create the list ab containing all the elements of the list a, followed by all the elements of the list b.
``````var
a,b,ab: TList;

...
ab := TList.Create;
ab.Assign(a);
...``````
167
Create the string t consisting of the string s with its prefix p removed (if s starts with p).
``````if AnsiStartsStr(p, s) then
t := copy(s, length(p)+1, length(s)-length(p))
else
s := t;``````
168
Create string t consisting of string s with its suffix w removed (if s ends with w).
``````if AnsiEndsStr(w, s) then
t := copy(s, 1, length(s) - length(w))
else
t :=s;``````
169
Assign to the integer n the number of characters of the string s.
Make sure that multibyte characters are properly handled.
n can be different from the number of bytes of s.
``n := length(s);``
Alternative implementation:
``n := Utf8Length(s);``
Alternative implementation:
``n := s.length;``
170
Set n to the number of elements stored in mymap.

This is not always equal to the map capacity.
``n := MyMap.Count;``
171
Append the element x to the list s.
``````var
L: TList;
Item: Pointer;
...
...``````
172
Insert value v for key k in map m.
``m.KeyData[k] := v;``
173
Number will be formatted with a comma separator between every group of thousands.
``writeln(format('%.0n',[double(10000)]));   ``
174
Make a HTTP request with method POST to the URL u
``````with TFPHTTPClient.Create(nil) do
begin
Post(u);
Free;
end;``````
175
From the array a of n bytes, build the equivalent hex string s of 2n digits.
Each byte (256 possible values) is encoded as two hexadecimal characters (16 possible values per digit).
``````s := '';
for b in a do s := s + IntToHex(b,2);``````
176
From hex string s of 2n digits, build the equivalent array a of n bytes.
Each pair of hexadecimal characters (16 possible values per digit) is decoded into one byte (256 possible values).
``````for i := 0 to length(s) div 2 - 1 do
a[i] := StrToInt('\$'+Copy(s,2*(i)+1,2));``````
177
Construct a list L that contains all filenames that have the extension ".jpg" , ".jpeg" or ".png" in directory D and all its subdirectories.
``L := FindAllFiles(D, '*.jpg;*.jpeg;*.png', True);``
178
Set boolean b to true if if the point with coordinates (x,y) is inside the rectangle with coordinates (x1,y1,x2,y2) , or to false otherwise.
Describe if the edges are considered to be inside the rectangle.
``b := PtInRect(Rect(x1,y1,x2,y2), Point(x,y));``
179
Return the center c of the rectangle with coördinates(x1,y1,x2,y2)
``c := CenterPoint(Rect(x1,y1,x2,y2));``
180
Create the list x containing the contents of the directory d.

x may contain files and subfolders.
No recursive subfolder listing.
``x := FindAllFiles(d, '*', False);``
Alternative implementation:
``````if FindFirst(IncludeTrailingPathDelimiter(d) + '*',
faAnyFile and (not faDirectory), SR) = 0 then
repeat
until FindNext(SR) <> 0;
FindClose(SR);
``````
182
Output the source of the current program. A quine is a computer program that takes no input and produces a copy of its own source code as its only output.

Reading the source file from disk is cheating.
``program Quine(Output);const A='program Quine(Output);const A=';B='begin writeln(A,char(39),A,char(39),char(59),char(66),char(61),char(39),B,char(39),char(59),B)end.';begin writeln(A,char(39),A,char(39),char(59),char(66),char(61),char(39),B,char(39),char(59),B)end.``
183
Make a HTTP request with method PUT to the URL u
``````with TFPHTTPClient.Create(nil) do
begin
Put(u);
Free;
end;``````
184
Assign to variable t a string representing the day, month and year of the day after the current date.
``````t := DateToStr(Now+1.0);
``````
186
Exit a program cleanly indicating no error to OS
``Halt;``
Alternative implementation:
``Application.Terminate;``
188
Perform matrix multiplication of a real matrix a with nx rows and ny columns, a real matrix b with ny rows and nz columns and assign the value to a real matrix c with nx rows and nz columns.
``````var
A: array[1..m, 1..n] of ArbFloat;
B: array[1..n, 1..p] of ArbFloat;
C: array[1..m, 1..p] of ArbFloat;

...

omvmmm(
A[1,1], m, n, n,
B[1,1], p, p,
C[1,1], p
);``````
189
Produce a new list y containing the result of the function T applied to all elements e of the list x that match the predicate P.
``````type
TListPredicate = function(e: pointer): Boolean;
TListElementFunc = function(e: pointer): pointer;

function NewList(X: TList; P: TListPredicate; T: TListElementFunc): TList;
var
e: pointer;
begin
Result := TList.Create;
for e in X do
begin
if P(e) then
end;
end;``````
190
Declare an external C function with the prototype

void foo(double *a, int n);

and call it, passing an array (or a list) of size 10 to a and 10 to n.

Use only standard features of your language.
``procedure foo(a: pdouble; n: integer); external 'some_c_dll' name 'foo'; cdecl;``
191
Given a one-dimensional array a, check if any value is larger than x, and execute the procedure f if that is the case
``for v in a do if v > x then f;``
193
Declare two two-dimensional arrays a and b of dimension n*m and m*n, respectively. Assign to b the transpose of a (i.e. the value with index interchange).
``````var
A: array[1..m, 1..n] of ArbFloat;
B: array[1..n, 1..m] of ArbFloat;
begin
... some code to fill A
omvtrm(
A[1,1], m, n, n,
B[1,1], m
);
end.``````
194
Given an array a, set b to an array which has the values of a along its second dimension shifted by n. Elements shifted out should come back at the other end.
``````type
TSomeType = Integer;
TArr = array of array of TSomeType;

...
procedure ShiftArr(src: TArr; var dest: TArr; n: Integer);
var
i,j,j2: integer;
begin
SetLength(dest, length(src), length(src[0]));
n := n mod length(src[0]);
for i := low(src) to high(src) do
begin
for j := low(src[0]) to high(src[0]) do
begin
j2 := j + n;
if j2 > high(src[0]) then
j2 := j2 - high(src[0]) - 1;
dest[i,j2] := src[i,j];
end;
end;
end;

...
ShiftArr(a,b,n);
...``````
195
Pass an array a of real numbers to the procedure (resp. function) foo. Output the size of the array, and the sum of all its elements when each element is multiplied with the array indices i and j (assuming they start from one).
``````procedure foo(a: array of double);
var
sum: double;
i: Integer;
begin
for i := low(a) to high(a) do
sum := sum + (i+1)*a[i];
writeln('Size = ',Length(a),', Sum = ',sum:6:5);
end;

...
foo(a);
...``````
196
Given an integer array a of size n, pass the first, third, fifth and seventh, ... up to the m th element to a routine foo which sets all these elements to 42.
``````procedure foo(var L: Integer);
begin
L := 42;
end;

begin
for i := 0 to Min(m, n-1) do
if not odd(i) then foo(a[i]);
end.``````
197
Retrieve the contents of file at path into a list of strings lines, in which each element is a line of the file.
``````var
Lines: TStringList;
...
Lines := TStringList.Create;
198
Abort program execution with error condition x (where x is an integer value)
``Runerror(x);``
199
Truncate a file F at the given file position.
``Truncate(F);``
200
Compute the hypotenuse h of the triangle where the sides adjacent to the square angle have lengths x and y.
``h := hypot(x,y);``
201
Calculate n, the Euclidean norm of data (an array or list of floating point values).
``````var
data: array of double;
...
n := norm(data);
...``````
202
Calculate the sum of squares s of data, an array of floating point values.
``````var
data: array of double;
...
s := SumOfSquares(data);
...``````
203
Calculate the mean m and the standard deviation s of the list of floating point values data.
``````var
m, s: double;
data: array of double;
...
MeanAndStdDev(data, m, s);
...``````
204
Given a real number a, print the fractional part and the exponent of the internal representation of that number. For 3.14, this should print (approximately)

0.785 2
``````var
d: double;
Mantissa: double;
Exponent: integer;
begin
d := 3.14;
frexp(d, Mantissa, Exponent);
writeln('Mantissa: ',Mantissa:6:5,', Exponent: ',Exponent);
end.``````
205
Read an environment variable with the name "FOO" and assign it to the string variable foo. If it does not exist or if the system does not support environment variables, assign a value of "none".
``````var
foo: string;
begin
foo := GetEnvironmentVariable('FOO');
if (foo = '') then foo := 'none';
end.``````
206
Execute different procedures foo, bar, baz and barfl if the string str contains the name of the respective procedure. Do it in a way natural to the language.
``````case str of
'foo': foo;
'bar': bar;
'baz': baz;
'barfl': barfl;
end;``````
207
Allocate a list a containing n elements (n assumed to be too large for a stack) that is automatically deallocated when the program exits the scope it is declared in.
``````var
a: array of some_type;
...
SetLength(a, n);
...``````
208
Given the arrays a,b,c,d of equal length and the scalar e, calculate a = e*(a+b*c+cos(d)).
Store the results in a.
``````for i := 0 to High(a) do
a[i] = e*(a[i]+b[i]*c[i]+cos(d[i]);``````
209
Declare a type t which contains a string s and an integer array n with variable size, and allocate a variable v of type t. Allocate v.s and v.n and set them to the values "Hello, world!" for s and [1,4,9,16,25], respectively. Deallocate v, automatically deallocating v.s and v.n (no memory leaks).
``````type
TDynIntArray = array of integer;
TT = record
s: string;
n: TDynIntArray;
end;
PTT = ^TT;

var
v: PTT;
begin
v := New(PTT);
v^.s := 'Hello world';
v^.n := TDynIntArray.Create(1,4,9,16,25);
Dispose(v);
end.``````
210
Assign, at runtime, the compiler version and the options the program was compilerd with to variables version and options, respectively, and print them. For interpreted languages, substitute the version of the interpreter.

Example output:

GCC version 10.0.0 20190914 (experimental)
-mtune=generic -march=x86-64
``writeln({\$I %fpcversion%});``
211
Create the folder at path on the filesystem
``MkDir(path);``
212
Set the boolean b to true if path exists on the filesystem and is a directory; false otherwise.
``b := DirectoryExists(path);``
213
Compare four strings in pair-wise variations. The string comparison can be implemented with an equality test or a containment test, must be case-insensitive and must apply Unicode casefolding.
``//no code here: see comments``
214
Append extra character c at the end of string s to make sure its length is at least m.
The length is the number of characters, not the number of bytes.
``s := UTF8PadRight(s,m,c);``
215
Prepend extra character c at the beginning of string s to make sure its length is at least m.
The length is the number of characters, not the number of bytes.
``s := UTF8PadLeft(s,m,c);``
216
Add the extra character c at the beginning and ending of string s to make sure its length is at least m.
After the padding the original content of s should be at the center of the result.
The length is the number of characters, not the number of bytes.

E.g. with s="abcd", m=10 and c="X" the result should be "XXXabcdXXX".
``s := UTF8PadCenter(s,m,c);``
217
Create a zip-file with filename name and add the files listed in list to that zip-file.
``````Zip := TZipper.Create;
Zip.FileName := name;
Zip.ZipAllFiles;
Zip.Free;
``````
218
Create the list c containing all unique elements that are contained in both lists a and b.
c should not contain any duplicates, even if a and b do.
The order of c doesn't matter.
``````for elem in a do
if (b.indexof(elem) >= 0) and (c.indexof(elem) = -1) then
219
Create the string t from the value of string s with each sequence of spaces replaced by a single space.

Explain if only the space characters will be replaced, or the other whitespaces as well: tabs, newlines.
``````var
i, j: integer;
t,s: string;
const
whitespace = [#32,#13,#10,#9];
begin
....
t := '';
j := 0;
setlength(t, length(s));
for i := 1 to length(s) do
if not ((s[i] in whitespace) and
((i < length(s)) and (s[i+1] in whitespace))) then
begin
inc(j);
t[j] := s[i];
end;
setlength(t,j);
end.``````
Alternative implementation:
``````  t := s;
while Pos('  ',t) > 0 do
t := StringReplace(t, '  ', ' ', [rfReplaceAll]);
``````
Alternative implementation:
``  t := ReplaceRegExpr('\s+',s,' ',False);``
220
Create t consisting of 3 values having different types.

Explain if the elements of t are strongly typed or not.
``````type
Tuple = record
a: integer;
b: string;
c: boolean;
end;
var
t: Tuple;
begin
t := Default(Tuple);
end.
``````
221
Create string t from string s, keeping only digit characters 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
``t := ReplaceRegExpr('[^\d]', s, ''); ``
Alternative implementation:
``````for i := 1 to length(s) do
if s[i] in ['0'..'9'] then
t := t + s[i];``````
222
Set i to the first index in list items at which the element x can be found, or -1 if items does not contain x.
``i := Items.IndexOf(x);``
223
Loop through list items checking a condition. Do something else if no matches are found.

A typical use case is looping through a series of containers looking for one that matches a condition. If found, an item is inserted; otherwise, a new container is created.

These are mostly used as an inner nested loop, and in a location where refactoring inner logic into a separate function reduces clarity.
``````Found := False;
for Item in Items do
begin
if Item.MatchesCondition then
begin
Found := True;
Break;
end;
end;
DoSomethingElse;``````
224
Insert the element x at the beginning of the list items.
``items.insert(0,x);``
225
Declare an optional integer argument x to procedure f, printing out "Present" and its value if it is present, "Not present" otherwise
``````procedure f; overload;
begin
writeln('not present');
end;

begin
writeln('present');
end;``````
226
Remove the last element from the list items.
``items.delete(items.count-1);``
227
Create the new list y containing the same elements as the list x.

Subsequent modifications of y must not affect x (except for the contents referenced by the elements themselves if they contain pointers).
``y.assign(x);``
228
Copy the file at path src to dst.
``Success := CopyFile(src, dst);``
229
Interrupt an ongoing processing p.
``````var
P: TProcess;
begin
...
P.Execute;
//do something else
P.Terminate(0);
end.``````
230
Cancel an ongoing processing p if it has not finished after 5s.
``````var
P: TProcess;
begin
...
P.Execute;
if not P.WaitOnExit(5000) then P.Terminate(0);
end.``````
231
Set b to true if the byte sequence s consists entirely of valid UTF-8 character code points, false otherwise.
``b := FindInvalidUTF8Codepoint(s) = -1;``
232
Print "verbose is true" if the flag -v was passed to the program command line, "verbose is false" otherwise.
``````for i in paramcount do
begin
if paramstr(i)='-v' then
begin
verbose := true;
break;
end;
writeln('verbose is ',verbose);
end.``````
233
Print the value of the flag -country passed to the program command line, or the default value "Canada" if no such flag was passed.
``````S := Application.GetOptionValue('country');
if S = '' then S := 'Canada';
writeln('Country = ',S);``````
234
Assign to the string s the standard base64 encoding of the byte array data, as specified by RFC 4648.
``s := EncodeStringBase64(data);``
235
Assign to byte array data the bytes represented by the base64 string s, as specified by RFC 4648.
``data := DecodeStringBase64(s, true);``
237
Assign to c the result of (a xor b)
``c := a xor b;``
238
Write in a new byte array c the xor result of byte arrays a and b.

a and b have the same size.
``````SetLength(c, Length(a));
for i := Low(a) to High(a) do c[i] := a[i] xor b[i];``````
239
Assign to string x the first word of string s consisting of exactly 3 digits, or the empty string if no such match exists.

A word containing more digits, or 3 digits as a substring fragment, must not match.
``````  with TRegExpr.Create do
begin
Expression := '\b\d\d\d\b';
Exec(s);
x := Match[0];
Free;
end;
``````
240
Lists a and b have the same length. Apply the same permutation to a and b to have them sorted based on the values of a.
``````type
TPairedList = class(TStringList)
private
FBuddy: TStrings;
protected
procedure ExchangeItems(Id1, Id2: Integer); override;
public
end;

procedure TPairedList.ExchangeItems(Id1, Id2: Integer);
begin
inherited Exchange(Id1, Id2);
if Assigned(FBuddy) then
FBuddy.Exchange(Id1, Id2);
end;

procedure TPairedList.Sort(Buddy: TStrings);
begin
FBuddy := Buddy;
Sort;
end;

begin
...
a.sort(b);
end.``````
241
Explicitly decrease the priority of the current process, so that other execution threads have a better chance to execute now. Then resume normal execution and call the function busywork.
``````TThread.Yield;
busywork;``````
242
Call a function f on each element e of a set x.
``for e in x do f(e);``
243
Print the contents of the list or array a on the standard output.
``for el in a do writeln(el);``
244
Print the contents of the map m to the standard output: keys and values.
``for APair in m do writeln(APair.Key, APair.Value);``
245
Print the value of object x having custom type T, for log or debug.
``writeln(x.T);``
246
Set c to the number of distinct elements in the list items.
``````function CountUniqueItems(Items: TStrings): Integer;
var
List: TStringList;
begin
List := TStringList.Create;
List.Duplicates := dupIgnore;
List.Sorted := True;
Result := List.Count;
List.Free;
end;

begin
...
c := CountUniqueItems(items);
...
end.``````
247
Remove all the elements from list x that don't satisfy the predicate p, without allocating a new list.
Keep all the elements that do satisfy p.

For languages that don't have mutable lists, refer to idiom #57 instead.
``````for i := x.count-1 downto 0 do
if not p(x.items[i]) then x.delete(i);``````
248
Construct the "double precision" (64-bit) floating point number d from the mantissa m, the exponent e and the sign flag s (true means the sign is negative).
``d.buildup(s, m, e);``
250
Choose a value x from map m.
m must not be empty. Ignore the keys.
``x := m.Data[Random(m.Count)]);``
251
Extract integer value i from its binary string representation s (in radix 2)
E.g. "1101" -> 13
``i := StrToInt('%'+s);``
252
Assign to the variable x the string value "a" if calling the function condition returns true, or the value "b" otherwise.
``````if condition then
x := a
else
x := b;``````
Alternative implementation:
``x := ifthen(condition, a, b);``
253
Print the stack frames of the current execution thread of the program.
``dump_stack(stdout,0);``
254
Replace all exact occurrences of "foo" with "bar" in the string list x
``````for i := 0 to x.count - 1 do
if x[i] = 'foo' then
x[i] := 'bar';``````
255
Print the values of the set x to the standard output.
The order of the elements is irrelevant and is not required to remain the same next time.
``for el in x do writeln(el);``
256
Print the numbers 5, 4, ..., 0 (included), one line per number.
``for i := 5 downto 0 do writeln(i);``
257
Print each index i and value x from the list items, from the last down to the first.
``for i := items.count-1 downto 0 do writeln(i,' ',items[i]);``
258
Convert the string values from list a into a list of integers b.
``````var
a: TStringList;
b: specialize TList<Integer>;
...
for i := 0 to a.count-1 do b.add(IntToStr(a[i]));``````
259
Build the list parts consisting of substrings of the input string s, separated by any of the characters ',' (comma), '-' (dash), '_' (underscore).
``parts := s.split([',','_','-']);``
260
Declare a new list items of string elements, containing zero elements
``items := TStringList.Create;``
261
Assign to the string x the value of fields (hours, minutes, seconds) of the date d, in format HH:MM:SS.
``````DefaultFormatSettings.TimeSeparator := ':';
DefaultFormatSettings.ShortTimeFormat := 'hh:mm:ss';
x := TimeToStr(d);
``````
262
Assign to t the number of trailing 0 bits in the binary representation of the integer n.

E.g. for n=112, n is 1110000 in base 2 ⇒ t=4
``````function Trail(n: Integer): Integer;
var
begin
T := 0;
while (T < SizeOf(Integer)*8) do
begin
if (n and Mask) <> 0 then Exit;
Inc(T);
end;
end;

begin
writeln(Trail(112),' (should be 4)');
end.``````
263
Write two functions log2d and log2u, which calculate the binary logarithm of their argument n rounded down and up, respectively. n is assumed to be positive. Print the result of these functions for numbers from 1 to 12.
``````function log2d(n: uint32): integer;
var
temp: uint32;
begin
Result := 0;
temp := 1;
while (temp < n) do
begin
Inc(Result);
temp := 1 shl Result;
end;
if (temp > n) then
Dec(Result);
end;

function log2u(n: uint32): integer;
begin
Result := log2d(n);
if (1 shl Result < n) then
Inc(Result);
end;

var
i: integer;
begin
for i := 1 to 16 do
writeln(i,': log2d = ',log2d(i),', log2u = ',log2u(i));
end.``````
264
Pass a two-dimensional integer array a to a procedure foo and print the size of the array in each dimension. Do not pass the bounds manually. Call the procedure with a two-dimensional array.
``````type
T2DArray = array of array of Integer;

procedure foo(A: T2DArray);
begin
writeln(Length(A),', ', Length(A[0]));
end;

var A: T2DArray;

begin
A := T2DArray.Create([1,2,3],[1,2,3]);
foo(A);  //prints 2, 3
end.``````
265
Calculate the parity p of the integer variable i : 0 if it contains an even number of bits set, 1 if it contains an odd number of bits set.
``````function Parity(n: Integer): Integer;
var
begin
Bits := 0;
for I := 0 to SizeOf(Integer)*8 - 1 do
begin
if ((n and Mask) <> 0) then Inc(Bits);
end;
Result := Ord(Odd(Bits));
end;

begin
writeln(Parity(42));
end.``````
Alternative implementation:
``````function Parity(n: Int32): Integer;
begin
Result := Ord(Odd(PopCnt(DWORD(n))));
end;

var
i: Int32;
begin
i := 42;
writeln('Parity(42) = ',Parity(i));
end.``````
266
Assign to the string s the value of the string v repeated n times, and write it out.

E.g. v="abc", n=5 ⇒ s="abcabcabcabcabc"
``````s:= '';
for i := 1 to n do s := s + v;
writeln(s);``````
Alternative implementation:
``````s := DupeString(v, n);
writeln(s);``````
267
Declare an argument x to a procedure foo that can be of any type. If the type of the argument is a string, print it, otherwise print "Nothing."

Test by passing "Hello, world!" and 42 to the procedure.
``````procedure foo(const x: variant);
begin
varOleStr, varUString, varString: writeln(x);
otherwise writeln('Nothing');
end;
end;

begin
foo('Hello World');
foo(42);
end.``````
269
Given the enumerated type t with 3 possible values: bike, car, horse.
Set the enum value e to one of the allowed values of t.
Set the string s to hold the string representation of e (so, not the ordinal value).
Print s.
``````  e := horse;
writestr(s, e);
writeln(e);``````
270
Given a floating point number r1 classify it as follows:
If it is a signaling NaN, print "This is a signaling NaN."
If it is a quiet NaN, print "This s a quiet NaN."
If it is not a NaN, print "This is a number."
``````  if r1.IsNan then
begin
if (TDoubleRec(r1).Data and \$4000000000000000) = \$4000000000000000 then
writeln('This is a quiet NaN')
else
writeln('This is a signalling NaN');
end
else
writeln('This is a number: ',r1);
``````
271
If a variable x passed to procedure tst is of type foo, print "Same type." If it is of a type that extends foo, print "Extends type." If it is neither, print "Not related."
``````procedure tst(x: tobject);
begin
if x.ClassType = foo then
writeln('Same type')
else if x is foo then
writeln('Extends type')
else
writeln('Not related');
end; ``````
272
Fizz buzz is a children's counting game, and a trivial programming task used to affirm that a programmer knows the basics of a language: loops, conditions and I/O.

The typical fizz buzz game is to count from 1 to 100, saying each number in turn. When the number is divisible by 3, instead say "Fizz". When the number is divisible by 5, instead say "Buzz". When the number is divisible by both 3 and 5, say "FizzBuzz"
``````for i := 1 to 100 do
begin
Fizz := (i mod 3) = 0;
Buzz := (i mod 5) = 0;
if Fizz then write('Fizz');
if Buzz then write('Buzz');
if not (Fizz or Buzz) then write(i);
write(' ');
end.``````
Alternative implementation:
``````program fizzbuzz;
{\$APPTYPE CONSOLE}
{\$R *.res}
uses
System.SysUtils;
var i: Integer;
begin
for i := 1 to 100 do
begin
if (i mod 3 = 0) and (i mod 5 = 0) then WriteLn(IntToStr(i) + ' = FizzBuzz')
else if (i mod 3 = 0) then WriteLn(IntToStr(i) + ' = Fizz')
else if (i mod 5 = 0) then WriteLn(IntToStr(i) + ' = Buzz')
else WriteLn(IntToStr(i));
end;
end.``````
273
Set the boolean b to true if the directory at filepath p is empty (i.e. doesn't contain any other files and directories)
``````with FindAllFiles(p, AllFilesMask, False) do
try
b := DirectoryExists(p) and (Count = 0);
finally
Free;
end;
``````
274
Create the string t from the string s, removing all the spaces, newlines, tabulations, etc.
``t := ReplaceRegExpr('\s', s, '');``
Alternative implementation:
``````  SetLength(t, Length(s));
i := 0;
for Ch in S do
if (Ch > #32) then
begin
Inc(i);
t[i] := Ch;
end;
SetLength(t, i);
``````
275
From the string s consisting of 8n binary digit characters ('0' or '1'), build the equivalent array a of n bytes.
Each chunk of 8 binary digits (2 possible values per digit) is decoded into one byte (256 possible values).
``````  Size := Length(S) div 8;
SetLength(a, Size);
for i := 0 to Size - 1 do
begin
SBin := '%' + Copy(S, 1+(i*8), 8);
Val(SBin, a[i], Err);
if (Err <> 0) then
RunError(106);
end;
``````
276
Insert an element e into the set x.
``Include(x,e);``
Alternative implementation:
``x := x + [e];``
277
Remove the element e from the set x.

Explains what happens if e was already absent from x.
``Exclude(x,e);``
Alternative implementation:
``x := x - [e];``
278
Read one line into the string line.

Explain what happens if EOF is reached.
``readln(line);``
279
Read all the lines (until EOF) into the list of strings lines.
``````while not EOF do
begin
end;``````
280
Remove all the elements from the map m that don't satisfy the predicate p.
Keep all the elements that do satisfy p.

Explain if the filtering happens in-place, i.e. if m is reused or if a new map is created.
``````for i := m.count-1 downto 0 do
if not p(m.items[i]) then m.delete(i);``````
283
Build the list parts consisting of substrings of input string s, separated by the string sep.
``parts := s.split([sep]); ``
284
Create a new list a (or array, or slice) of size n, where all elements are integers initialized with the value 0.
``````a := nil;
setlength(a, n);``````
285
Given two floating point variables a and b, set a to a to a quiet NaN and b to a signalling NaN. Use standard features of the language only, without invoking undefined behavior.
``a := NaN;``
286
Print a line "Char i is c" for each character c of the string s, where i is the character index of c in s (not the byte index).

Make sure that multi-byte characters are properly handled, and count for a single character.
``````for i := 1 to utf8length(s) do
writeln(format('Char %d is %s',[i, utf8copy(s,i,1)]));``````
287
Assign to n the number of bytes in the string s.

This can be different from the number of characters. If n includes more bytes than the characters per se (trailing zero, length field, etc.) then explain it. One byte is 8 bits.
``n := length(s);``
288
Set the boolean b to true if the set x contains the element e, false otherwise.
``b := e in x;``
289
Create the string s by concatenating the strings a and b.
``s := a + b;``
291
Delete all the elements from index i (included) to index j (excluded) from the list items.
``````for index := j-1 downto i do
items.delete(index);``````
292
Write "Hello World and 你好" to standard output in UTF-8.
``````  {\$IFDEF WINDOWS}
SetTextCodePage(Output, CP_UTF8);
SetConsoleOutputCP(CP_UTF8);
{\$ENDIF}
writeln('Hello World and 你好');``````
293
Create a new stack s, push an element x, then pop the element into the variable y.
``````s := TStack.Create;
s.Push(x);
y := s.Pop;
``````
294
Given an array a containing the three values 1, 12, 42, print out
"1, 12, 42" with a comma and a space after each integer except the last one.
``````var
a: array of integer;
i: Integer;
begin
a := [1,12,42];
for i := Low(a) to High(a) do
begin
write(a[i]);
if i <> High(a) then write(', ');
end;
end.``````
295
Given the enumerated type T, create a function TryStrToEnum that takes a string s as input and converts it into an enum value of type T.

Explain whether the conversion is case sensitive or not.
Explain what happens if the conversion fails.
``````function TryEnumToStr(const s: string; out enum: T): Boolean;
var
code: integer;
begin
Val(s, enum, code);
Result := (code = 0);
end;``````
296
Assign to x2 the value of string x with the last occurrence of y replaced by z.
If y is not contained in x, then x2 has the same value as x.
``````  x2 := x;
p := RPos(y, x);
if (p > 0) then
begin
Delete(x2, p, Length(y));
Insert(z, x2, p);
end;
``````
Alternative implementation:
``````  x2 := ReverseString(StringReplace(ReverseString(x), ReverseString(y), ReverseString(z), []));
``````
297
Sort the string list data in a case-insensitive manner.

The sorting must not destroy the original casing of the strings.
``data.sort;``
299

This line will not be compiled or executed.
``// a line of comments, this line will not be compiled or executed.``
301
Compute the Fibonacci sequence of n numbers using recursion.

Note that naive recursion is extremely inefficient for this task.
``````function fib(n: word): uint64;
begin
if (n in [0,1]) then
result := n
else
result := fib(n-2) + fib(n-1);
end; ``````
302
Given the integer x = 8, assign to the string s the value "Our sun has 8 planets", where the number 8 was evaluated from x.
``s := Format('Our sun has %d planets',[x]);``
Alternative implementation:
``s := 'Our sun has '+IntToStr(x)+' planets';``
Alternative implementation:
``s := 'Our sun has '+x.ToString+' planets';``
303
Declare an array a of integers with six elements, where the first index is 42 and consecutive elements have the indices 43, 44, 45, 46, 47.
``````var
a: array[42..47] of integer;``````
304
Create the array of bytes data by encoding the string s in UTF-8.
``````var
data: pbyte absolute s;``````
305
Compute and print a^b, and a^n, where a and b are floating point numbers and n is an integer.
``````writeln('a^b=',power(a,b));
writeln('a^n=',power(a,n));``````
306
Preallocate memory in the list x for a minimum total capacity of 200 elements.

This is not possible in all languages. It is only meant as a performance optimization, should not change the length of x, and should not have any effect on correctness.
``x.capacity := 200;``
Alternative implementation:
``SetLength(a, 200);``
307
Create a function that XOR encrypts/decrypts a string
``encrypted := xorstring(key, original);``
308
Create the string representation s of the integer value n in base b.

18 in base 3 -> "200"
26 in base 5 -> "101"
121 in base 12 -> "a1"

``````function IntToBaseStr(n: longword; const b: cardinal): string;
const
digits = '0123456789abcdefghijklmnopqrstuvwxyz';
var
remainder: longword;
begin
Result := '';
repeat
DivMod(n, b, n, remainder);
result := digits[remainder + 1] + result;
until n = 0;
end;``````
Alternative implementation:
``s := IntToStrBase(n,b);``
309
Create the new 2-dimensional array y containing a copy of the elements of the 2-dimensional array x.

x and y must not share memory. Subsequent modifications of y must not affect x.
``y := x;``
Alternative implementation:
``y := copy(x, Low(x), Length(x));``
310
Fill the byte array a with randomly generated bytes.
``for b in a do b := random(256);``
311
Create the new object y by cloning the all the contents of x, recursively.
``````var
x,y: TPersistent;
...
y.assign(x);
...``````
312
Set b to true if the lists p and q have the same size and the same elements, false otherwise.
``````  b := (p.count = q.count);
if b then for i := 0 to p.count-1 do
if (p.items[i] <> q.items[i]) then
begin
b := false;
break;
end;``````
314
Set all the elements in the array x to the same value v
``for i := Low(x) to High(x) do x[i] := v;``
316
Determine the number c of elements in the list x that satisfy the predicate p.
``````  c := 0;
for el in x do if p(el) then Inc(c);``````
317
Create a string s of n characters having uniform random values out of the 62 alphanumeric values A-Z, a-z, 0-9
``````function RandomString(Size: Integer): String;
const
Chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
Len = Length(Chars);
var
i: Integer;
begin
Result := '';
SetLength(Result, Size);
for i := 1 to Size do
begin
Result[i] := Chars[Random(Len)+1];
end;
end; ``````
320
Set b to true if the string s is empty, false otherwise
``b := (s = '');``
321
Assign to c the value of the i-th character of the string s.

Make sure to properly handle multi-byte characters. i is the character index, which may not be equal to the byte index.
``c := Utf8Copy(s,i,1);``
Alternative implementation:
``c := s[i];``
322
``````generic function replace<T>(var X: T; NewValue: T):T;
begin
Result := X;
X := NewValue;
end;

begin
x := someoldvalue;
y := specialize replace<TSomeType>(x, somenewvalue);
end.``````
325
Create a new queue q, then enqueue two elements x and y, then dequeue an element into the variable z.
``````type
TQ = specialize TQueue<TSomeType>;
var
x, y, z: TSomeType;
Q: TQ;

begin
Q := TQ.Create;
Q.Push(x);
Q.Push(y);
z := Q.Front;
Q.Pop;
Q.Free;
end.
``````
326
Assign to t the number of milliseconds elapsed since 00:00:00 UTC on 1 January 1970.
``t := DateTimeToUnix(Now);``
327
Assign to t the value of the string s, with all letters mapped to their lower case.
``t := LowerCase(s);``
328
Assign to t the value of the string s, with all letters mapped to their upper case.
``t := UpperCase(s);``
336
Compute x = b

b raised to the power of n is equal to the product of n terms b × b × ... × b
``X := Power(B, N);``
337
Extract the integer value i from its string representation s, in radix b
``i := StrToInt64Base(s, b);``
339
Set all the elements of the byte array a to zero
``FillByte(a, Length(a), 0);``
340
Assign to c the value of the last character of the string s.

Explain the type of c, and what happens if s is empty.

Make sure to properly handle multi-bytes characters.
``````function GetLastUtfCodePoint(const S: String): String;
var
p: PChar;
PLen: PtrInt;
begin
Result := '';
p := UTF8CodepointStart(PChar(S), Length(S), Utf8Length(S) - 1);
PLen := UTF8CodepointSize(p);
Result := p;
SetLength(Result,PLen);
end;

var
s: string;
begin
c := GetLastUtfCodePoint(s);
end.``````
Alternative implementation:
``c := s[Length(s)];``
341
Set i to the position of the last occurrence of the string y inside the string x, if exists.

Specify if i should be regarded as a character index or as a byte index.

Explain the behavior when y is not contained in x.
``i := RPos(y,x);``
342
Determine if the current year is a leap year.
``if IsLeapYear(SomeYear) then writeln('SomeYear is a leap year')``
343
Rename the file at path1 into path2
``if RenameFile(path1,path2) then writeln('Ok');``
344
Assign to ext the fragment of the string f after the last dot character, or the empty string if f does not contain a dot.

E.g. "photo.jpg" -> "jpg"

ext must not contain the dot character.
``````ext := ExtractFileExt(f);
if (ext <> '') then system.delete(ext,1,1);``````
346
Create the list y from the list x repeated n times
``````y := TList.Create;
for i := 1 to n do y.AddList(x);``````