Relearning C - Chapter 4

Chapter 4 - Functions and Program Structure

Functions break large computing tasks into smaller ones, and enable people to build on what others have done instead of starting over from scratch.

4.1 Basics of Functions

Design and write a program to print each line of its input that contains a particular pattern, or string of characters. For example, searching for the pattern of letters “ould” in the set of lines.

Ah Love! could you and I with Fate conspire 
To grasp this sorry Scheme of Things entire, 
Would not we shatter it to bits -- and then 
Re-mould it nearer to the Heart's Desire! 

will produce the output…

Ah Love! could you and I with Fate conspire
Would not we shatter it to bits -- and then
Re-mould it nearer to the Heart's Desire!

The job falls neatly into three pieces:

while (there is another line)
    if (the line contains the pattern)
        print it

Here goes the code.

#include <stdio.h>
#define MAXLINE 1000

int getline(char line[], int max)
int strindex(char source[], char searchfor[]);

char pattern[] = "ould";

main() {
    char line[MAXLINE];
    int found = 0;

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

int getline(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;
    }
}

int strindex(char s[], char t[]) {
    int i, j, k;

    for (i = 0; s[i] != '\0'; i++) {
        for (j = i, k = 0; t[k] != '\0' && s[j] == t[k]; j++, k++) {
            ;
        }
        if (k > 0 && t[k] == '\0') {
            return i;
        }
    }
    return -1;
}