4.7 (StrStr)

//https://vk.com/evgenykravchenko0

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char *strstr(const char* str, const char* substr )
{
    const char* p;

    for ( p = str; *p; ++p )
        if ( *p == *substr )
            return (char*)p;
    return 0;
}
#include <stdio.h>

void find_str(char const* str, char const* substr)
{
  char* pos = strstr(str, substr);
    if(pos)
    {
      printf("found the string '%s' in '%s' at position: %ld\n", substr, str, pos - str);
    }
    else
    {
      printf("the string '%s' was not found in '%s'\n", substr, str);
    }
}

int main(void)
{
  char* str = "H E L L O";
  find_str(str, "H");
  find_str(str, "E");
  find_str(str, "L");

  return 0;
}