Question

Write a function to check whether string s1 is a substring of string s2. The function returns the first index in s2 if there is a match. Otherwise, return -1. For example, the function should return 2 if s1 is "to" and s2 is "October". If s1 is "andy" and s2 is "candy", then the function should return 1. The function prototype is as follows:

int indexOf(const char *s1, const char *s2)

Write a program to test the function.

Answer 1

#include <stdio.h>

int indexOf(const char *s1, const char *s2);

int main() {
    printf("%d\n", indexOf("to", "October"));
    printf("%d\n", indexOf("andy", "candy"));
    printf("%d\n", indexOf("hi", "hello"));
    return 0;
}

int indexOf(const char *s1, const char *s2) {
    int i = 0, j;
    while (s2[i]) {
        j = 0;
        while (s1[j]) {
            if (s1[j] != s2[i+j])
                break;
            j++;
        }
        if (s1[j] == 0)
            return i;
        i++;
    }
    return -1;
}