Ccheck string1 in string 2

// C program to check if a string is
// substring of other.
#include <stdio.h>
#include <string.h>

// Function to find if S1 is a substring of S2
int findSubstring(char S1[], char S2[]) {
    int M = strlen(S1);
    int N = strlen(S2);

    // Iterate through S2
    for (int i = 0; i <= N - M; i++) {
      
        // Check for substring match
        int j;
        for (j = 0; j < M; j++) {
          
          // Mismatch found
            if (S2[i + j] != S1[j]) {
                break; 
            }
        }
      
        // If we completed the inner loop, we found a match
        if (j == M) {
          // Return starting index
            return i; 
        }
    }
    // No match found
    return -1; 
}

int main() {
    char S1[] = "for";
    char S2[] = "geeksforgeeks";
    int result = findSubstring(S1, S2);
    
    if (result != -1) {
        printf("%d", result);
    } else {
        printf(-1);
    }

    return 0;
}