C_PRG_LANG_EX_2.4

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

char *squeeze(char *s1, char *s2)
{
    int size = 0;
    for(int i = 0; s1[i] != '\0'; i++, size++)
        ;

    for(int i = 0; s1[i] != '\0'; i++)
    {
        for(int j = 0; s2[j] != '\0'; j++)
        {
            if (s1[i] == s2[j])
            {
                for(int k = i; k < size; k++)
                    s1[k] = s1[k + 1];

                i--;
                size--;
                break;
            }
        }
    }

    return s1;
}

int main(void)
{
    char *str1 = malloc(sizeof(char) * 256);
    char *str2 = malloc(sizeof(char) * 256);
    strcpy(str1, "Mother washed the window");
    strcpy(str2, "Mother washed the window");
    printf("%s\n%s\n", str1, str2);
    str1 = squeeze(str1, str2);
    printf("%s\n", str1);
    free(str1);
    free(str2);
    return 0;
}