Exercise 2.4 - Compare S1, S2 To Delete Same Character in S1

Question

Write an alternative version of squeeze(s1,s2) that deletes each character in s1 that matches any character in the string s2.

/**
 * Exercise 2.4
 *
 * Let us write a version of squeeze(s1,s2) that deletes each
 * character in the string 1 that matches any character in the string s2.
 * Utilize user defined function mgetline to input the strings.
 * Don't use any standard library string manipulation function.
 *
 **/

#include <stdio.h>

#define MAXLINE 1000

int mgetline(char s[], int lim);

void squeeze(char s1[], const char s2[]);

int main(void) {
    char s1[MAXLINE], s2[MAXLINE];
    mgetline(s1, MAXLINE);
    mgetline(s2, MAXLINE);

    squeeze(s1, s2);

    printf("\n%s\n", s1);

    return 0;
}

int mgetline(char s[], int lim) {
    int i, c;

    for (i = 0; i < lim - 1 && (c = getchar()) != EOF && c != '\n'; ++i)
        s[i] = c;

    if (c == '\n')
        s[i++] = c;

    s[i] = '\0';

    return i;
}

void squeeze(char s1[], const char s2[]) {
    int i, j, k;
    k = 0;

    for (i = 0; s1[i] != '\0'; ++i) {
        for (j = 0; (s1[i] != s2[j]) && s2[j] != '\0'; ++j)
            ;
        if (s2[j] == '\0')
            s1[k++] = s1[i];
    }

    s1[k] = '\0';
}

Explanation

Let’s take the two inputs strings as:

HelloWorld
ol

Our desired output is

HeWrd

This has removed the characters o and l from the first string. The way squeeze works is, it take each character from the first string and if there is no match found, stores it with a new index k. If there is a match found in s2, it simply skips it. The way it skips is realized by the following

for(j=0; (s1[i]!=s2[j]) && s2[j]!='\0' ;++j)
    ;
if(s2[j]=='\0')
    s1[k++] = s1[i];

When the match is found s1[i] == s2[j] so our first for loop will end. The second if condtion will fail too as s2 is not iterated till the end, so we do not place the character in s1[k++] and we have successfully skipped it.

Visualization

Try It Out