strstr
#include <stdio.h>
#include <string.h>
int main() {
const char *haystack = "Hello, world! This is a sample string.";
const char *needle = "world";
char *result = strstr(haystack, needle);
if (result != NULL) {
printf("'%s' found at index %ld\n", needle, result - haystack);
} else {
printf("'%s' not found in the string.\n", needle);
}
return 0;
}