Exercise4-1.c

/*Exercise 4-1. Write the function strindex(s,t) 
which returns the position of the rightmost occurrence 
of t in s, or -1 if there is none.*/

#include <stdio.h>
#include <string.h>
#define MAXLINE 1000 /* maximum input line length */

int get_line(char line[], int max);
int strindex(char source[], char searchfor[]);
char pattern[] = "program";     /* pattern to search for */

/* find all lines matching pattern */
int main()
{
    char line[MAXLINE];
    int found = 0;

    while (get_line(line, MAXLINE) > 0)
        if (strindex(line, pattern) >= 0)
        {
            printf("%s", line);
            found++;
        }
    return found;
}

/* getline: get line into s, return length */
int get_line(char s[], int lim)
{
    int c, i;
    i = 0;
    while (--lim > 0 && (c=getchar()) != EOF && c != '\n')
        s[i++] = c;
    if (c == '\n')
        s[i++] = c;
    s[i] = '\0';
    return i;
}

/* strindex: return index of t in s, -1 if none */
int strindex(char s[], char t[])
{
    int i, j, k;

    for (i = strlen(s)-1;  i>=0; i--)
    {
        for (j=i, k=strlen(t)-1; s[j]==t[k]; j--, k--)
            if (k == 0 )
                return i;
    }

    return -1;
}