Exercise 4.1 from K&R C book

strrindex.c

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

int strrindex(char *s, char *t);

int main(void)
{
    char items[] = "bartbartbart";
    char items2[] = "rt";
    printf("%d", strrindex(items, items2));
}

int strrindex(char *s, char *t)
{
    int n = strlen(s);
    int d = strlen(t);
    int res = 0;

    for (int i = n - 1; i >= 0; i--)
    {
        for (int j = d - 1; j >= 0; j--)
        {
            if (s[i] == t[j])
            {
                ++res;
            }
            if (res == d)
            {
                return i;
            }
        }
    }
    return -1;
}