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.
New implementation

Be concise.

Be useful.

All contributions dictatorially edited by webmasters to match personal tastes.

Please do not paste any copyright violating material.

Please try to avoid dependencies to third-party libraries and frameworks.

Other implementations
#include <string.h>
int i=(int)(x-strstr(x,y));
#include <string>
int i = x.find(y);
var i = x.IndexOf(y);
import std.algorithm;
auto i = x.countUntil(y);
var i = x.indexOf(y);
import "strings"
i := strings.Index(x, y)
import Data.List
Just i <- (y `isPrefixOf`) `findIndex` (tails x)
let i = x.indexOf(y);
int i = x.indexOf(y);
i = x:find(y)
$i = mb_strpos($x, $y, 0, 'UTF-8');
i := Pos(y, x);
$i = index($x, $y);
i = x.find(y)
i = x.index(y)
let i = x.find(y);