Puzzle S15

Find first substring

[H-8]Write function that finds the first occurance of a substring in another (usually larger) source string. If the substring is found, a pointer to the beginning of the first occurance in the source string is returned. If the substring is not found, NULL is returned. Here is a testing program:

/* Puzzle S15 --  Find Substring */
#include <stdio.h>
#include <stdlib.h>

int startsWith( char const *bigString, char const *start )
{
}

char *findSubstring( char const *source, char const *sub )
{
}

int main(int argc, char *argv[])
{
 char *trials[][2] =
  {
    {"abcdef", "a"},
    {"abcdef", "abc"},
    {"abcdef", "d"},
    {"abcdef", "def"},
    {"abcdef", "f"},
    {"abcdef", "xyz"},
    {"abcdef", "axx"},
    {"abcdef", "abcdefg"},
    {"abcdef", "rats"},
    {"abbccddeef", "cc"},
    {"abcdefg", "g"},
    {"applecart", "c"},
    {"green", "apple"},
    {"apple", ""},
    {"", "rats"},
    {"",""}
  };

  int j; char *loc;
  for ( j=0; j<sizeof(trials)/sizeof(trials[0]); j++ )
  {
    loc = findSubstring( trials[j][0], trials[j][1] );
    if ( loc )
      printf("%s : %s : %s\n", trials[j][0], trials[j][1], loc );
    else
      printf("%s : %s : %s\n", trials[j][0], trials[j][1], "not found" );
  }

  return 0;

It will be useful to write this function using your startsWith() function.

Note: this function is similar to the standard function strstr().