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Programming-Idioms

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  • Python
  • Fortran

Idiom #43 Break outer loop

Look for a negative value v in 2D integer matrix m. Print it and stop searching.

Control flow jumping forward after the end of the outermost loop 
  outer: do j=1, size(m,2)
     do i=1, size(m,1)
        v = m(i,j)
        if (v < 0) then
           print *,v
           exit outer
        end if
     end do
  end do outer
OUTER:
for (var i in m) {
   for (var j in m[i]) {
      if (m[i][j] < 0) {
         console.log("Negative value found: "+m[i][j]);
         break OUTER;
      }
   }
}
from itertools import chain
matrix = [[1,2,3],[4,-5,6],[7,8,9]]
try:
    print(next(i for i in chain.from_iterable(matrix) if i < 0))
except StopIteration:
    pass

We make a generator that will return negative values from a list (and use chain.from_iterable(matrix) to lazily extract the values) and only take one value from it with the next function. The generator will not continue until we call next again.

This will raise StopIteration if it doesn't find the value so we need to account for it.
class BreakOuterLoop (Exception): pass

try:
    position = None
    for row in m:
        for column in m[row]:
            if m[row][column] == v:
                position = (row, column)
                raise BreakOuterLoop
except BreakOuterLoop:
    pass

This is ugly because the pythonic way to solve this problem would be to refactor so that one doesn't have to break out of multiple loops. See PEP3136
def loop_breaking(m, v): 
    for i, row in enumerate(m): 
        for j, value in enumerate(row): 
            if value == v: 
                return (i, j)
    return None

print(loop_breaking(([1,2,3],[4,5,6],[7,8,9]), 6))

Rather than set break flags, it is better to refactor into a function, then use return to break from all nested loops.
z = False
for a in m:
    for b in a:
        if z := b < 0:
            print(b)
            break
    if z: break
Outer_loop:
for A in M'Range (1) loop
   Inner_Loop:
   for B in M'Range (2) loop
      if M (A, B) < 0 then
         Put_Line (M (A, B)'Image);
         exit Outer_Loop;
      end if;
   end loop Inner_Loop;
end loop Outer_Loop;
New implementation...
< > ⌨
programming-idioms.org 
  outer: do j=1, size(m,2)
     do i=1, size(m,1)
        v = m(i,j)
        if (v < 0) then
           print *,v
           exit outer
        end if
     end do
  end do outer
OUTER:
for (var i in m) {
   for (var j in m[i]) {
      if (m[i][j] < 0) {
         console.log("Negative value found: "+m[i][j]);
         break OUTER;
      }
   }
}
matrix = [[1,2,3],[4,-5,6],[7,8,9]]
try:
    print(next(i for i in chain.from_iterable(matrix) if i < 0))
except StopIteration:
    pass
class BreakOuterLoop (Exception): pass

try:
    position = None
    for row in m:
        for column in m[row]:
            if m[row][column] == v:
                position = (row, column)
                raise BreakOuterLoop
except BreakOuterLoop:
    pass
def loop_breaking(m, v): 
    for i, row in enumerate(m): 
        for j, value in enumerate(row): 
            if value == v: 
                return (i, j)
    return None

print(loop_breaking(([1,2,3],[4,5,6],[7,8,9]), 6))
z = False
for a in m:
    for b in a:
        if z := b < 0:
            print(b)
            break
    if z: break
Outer_loop:
for A in M'Range (1) loop
   Inner_Loop:
   for B in M'Range (2) loop
      if M (A, B) < 0 then
         Put_Line (M (A, B)'Image);
         exit Outer_Loop;
      end if;
   end loop Inner_Loop;
end loop Outer_Loop;
int i,j;
for(i=0;i<sizeof(m)/sizeof(*m);i++)
{
	for(j=0;j<sizeof(*m)/sizeof(**m);j++)
	{
		if(m[i][j]<0)
		{
			printf("%d\n",m[i][j]);
			goto end;
		}
	}
}
end:
(loop [rows m]
  (if-let [v (some #(when (neg? %) %) (first rows))]
    v
    (recur (rest rows))))
auto indices = findNegativeValue (m, 10, 20);
std::cout << m[indices.first][indices.second] << '\n';

std::pair<int, int> findNegativeValue (int **m, int rows, int columns) {
  for (int i = 0; i < rows; ++i) {
    for (int j = 0; j < columns; ++j) {
      if (m[i][j] < 0) return make_pair (i, j);
    }
  }
  throw "No negative value!";
}
for (
        int i = 0,
        rows = m.GetLength(0),
        cols = m.GetLength(1); i < rows; i++)
{
    for (int j = 0; j < cols; j++)
    {
        if (m[i, j] < 0)
        {
            Console.WriteLine(m[i, j]);
            i = int.MaxValue - 1; // Break outer loop.
            break;
        }
    }
}
foreach (int v in m)
{
    if (v < 0)
    {
        Console.WriteLine(v);
        break;
    }
}
foreach (int[] row in m)
{
    foreach (int v in row)
    {
        if (v < 0)
        {
            Console.WriteLine(v);
            goto DONE;
        }
    }
}
DONE: ;
bool keepLooping = true;

for(int i = 0; i < m.length && keepLooping; i++)
{
	for(int j = 0; j < m[i].length && keepLooping; j++)
	{
		if(m[i][j] < 0)
		{
			Console.WriteLine(m[i][j]);
			keepLooping = false;
		}
	}
}
outer:
foreach (i; 0 .. m.length)
{
	foreach (j; 0 .. m[i].length)
	{
		if (m[i][j] < 0)
		{
			writeln(m[i][j]);
			break outer;
		}
	}
}
OUTER: for (var i = 0; i < m.length; i++) {
  for (var j = 0; j < m[i].length; j++) {
    if (m[i][j] < 0) {
      print("Negative value found at $i,$j: ${m[i][j]}");
      break OUTER;
    }
  }
}
  def main([]), do: nil
  def main([row | rows]), do: main(row, rows)
  def main([], rows), do: main(rows)
  def main([number | numbers], rows) when number >= 0, do: main(numbers, rows)
  def main([number | _], _), do: number
find_negative_in([]) -> undefined;
find_negative_in([Row|Rows]) -> find_negative_in(Row, Rows).

find_negative_in([], Rows) -> find_negative_in(Rows);
find_negative_in([Pos|Values], Rows) when Pos >= 0 ->
	find_negative_in(Values, Rows);
find_negative_in([Neg|_], _) -> Neg.
mainloop:
	for i, line := range m {
		for _, v := range line {
			if v < 0 {
				fmt.Println(v)
				break mainloop
			}
		}
	}
(print . head . filter (<0) . concat) m

   int i, j, M = m.length, N = m[0].length, x;
a: for (i = 0; i < M; ++i)
       for (j = 0; j < N; ++j)
           if ((x = m[i][j]) < 0) {
               out.println(x);
               break a;
           }
int i, j, M = m.length, N = m[0].length, x;
boolean b = false;
for (i = 0; i < M; ++i) {
    for (j = 0; j < N; ++j)
        if ((x = m[i][j]) < 0) {
            out.println(x);
            b = true;
            break;
        }
    if (b) break;
}
mainloop: for(int i=0;i<m.length;i++)
	for(int j=0;j<m[i].length;j++)
		if(m[i][j]<0){
			System.out.println(m[i][j]);
			break mainloop;
		}
loop@ for (x in 0..7) {
  for (y in 0..7) {
    val v = m[x][y]
    if ( v < 0) {
       println("found a negative value at [$x][$y]: $v")
       break@loop
     }
  }
}
(loop named outer
      for i below (array-dimension m 0)
      do (loop for j below (array-dimension m 1)
               for v = (aref m i j)
               when (minusp v)
               do (progn
                    (print v)
                    (return-from outer))))
for _,v1 in ipairs(m) do
 for _,v2 in ipairs(v1) do
  if v2<0 then
   print(v2)
   goto outer
  end
 end
end
::outer::
breakout = false
for i,v1 in ipairs(m) do
   for j,v2 in ipairs(v1) do
      if v2 < 0 then
         print(v2)
         state = "found"
         breakout = true
         break
      end
   end
   if breakout then break end
end
[m enumerateObjectsUsingBlock:^(NSArray *row, NSUInteger rn, BOOL *stopr) {
  [row enumerateObjectsUsingBlock:^(NSNumber *v, NSUInteger cn, BOOL *stopc) {
    if (v.intValue<0) {
      NSLog(@"found %@ at row:%lu col:%lu",v,rn,cn);
      *stopr=*stopc=YES;
      return; // to quit the current block immediately
    }
  }];
}];

for ($y = 0; $y < count($m); $y++) {
    for ($x = 0; $x < count($m[$y]); $x++) {
        if ($m[$y][$x] == $v) {
            break 2;
        }
    }
}
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;

OUTER: for my $row (@m) {
   INNER: for my $v (@$row) {
      if ($v < 0) {
         print "Negative value found: $v\n";
         last OUTER;
      }
   }
}
negative_value = catch :negative do
  matrix.each do |row|
    row.each do |value|
      throw :negative, value if value < 0
    end
  end
end

puts negative_value
'outer: for v in m {
    'inner: for i in v {
        if i < 0 {
            println!("Found {}", i);
            break 'outer;
        }
    }
}
| negativeValue |
negativeValue := [ :matrix || ctx |
    ctx := thisContext sender.
    matrix do: [ :row |
        row do: [ :value |
            (value < 0) ifTrue: [ ctx resumeWith: value ].
        ]
    ]
] value: m. "ex. m := #((1 2 -1 3))"
Transcript show: negativeValue; cr.
For i As Integer = 0 To m.GetLength(0) - 1
    For j As Integer = 0 To m.GetLength(1) - 1
        If m(i, j) < 0 Then
            Console.WriteLine(m(i, j))
            i = Integer.MaxValue - 1 ' Break outer loop.
            Exit For
        End If
    Next
Next
Select Case Nothing
    Case Else
        For Each row As Integer() in m
            For Each v As Integer In row
                If v < 0 Then
                    Console.WriteLine(v)
                    Exit Select
                End If
            Next
        Next
End Select
    For Each row As Integer() in m
        For Each v As Integer In row
            If v < 0 Then
                Console.WriteLine(v)
                GoTo DONE
            End If
        Next
    Next
DONE:
Dim colCount As Integer = m(0).Length
For Each row As Integer() In m
    Dim j = 0
    Do While j < colCount
        Dim v = row(j)
        If v < 0 Then
            Console.WriteLine(v)
            Exit For
        End If
        j += 1
    Loop
Next