Check substring exists in a string in C

if (strstr(sent, word) != NULL) {
    /* ... */
}

Note that strstr returns a pointer to the start of the word in sent if the word word is found.

Use strstr for this.

http://www.cplusplus.com/reference/clibrary/cstring/strstr/

So, you'd write it like..

char *sent = "this is my sample example";
char *word = "sample";

char *pch = strstr(sent, word);

if(pch)
{
    ...
}

Try to use pointers...

#include <stdio.h>
#include <string.h>

int main()
{

  char str[] = "String1 subString1 Strinstrnd subStr ing1subString";
  char sub[] = "subString";

  char *p1, *p2, *p3;
  int i=0,j=0,flag=0;

  p1 = str;
  p2 = sub;

  for(i = 0; i<strlen(str); i++)
  {
    if(*p1 == *p2)
      {
          p3 = p1;
          for(j = 0;j<strlen(sub);j++)
          {
            if(*p3 == *p2)
            {
              p3++;p2++;
            } 
            else
              break;
          }
          p2 = sub;
          if(j == strlen(sub))
          {
             flag = 1;
            printf("\nSubstring found at index : %d\n",i);
          }
      }
    p1++; 
  }
  if(flag==0)
  {
       printf("Substring NOT found");
  }
return (0);
}