Question

So I’m trying to do the practice exercises in K&R. It wants me to make a function similar to squeeze, I don’t get whats wrong with it. I desk checked it already. I don’t want a solution found on the net, I wanna understand why my code wont work.

//removes characters that are present in both strings
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#define MAXLTR 15

void removesame(char s1[],char s2[]);

int main(void)
{
    char string1[MAXLTR],string2[MAXLTR];
    printf("Enter a string: ");
    scanf("\n%s",&string1);
    printf("\nEnter the letters/words to be removed: ");
    scanf("\n%s",&string2);
    removesame(string1,string2);
    printf("\nFinal output: %s",string1);
    getch();
}

void removesame(char s1[],char s2[])
{
    char temp[MAXLTR];
    int arraycntr,comparecntr;
    for(comparecntr = 0; comparecntr < MAXLTR; comparecntr++)
    {
        for(arraycntr = 0;arraycntr < MAXLTR;arraycntr++)
        {
            if(s1[arraycntr] == s2[arraycntr])
                s1[arraycntr] == '\t';
        }
    }
    comparecntr = 0;
    for(arraycntr = 0; arraycntr < MAXLTR; arraycntr++)
    {
        if(s1[arraycntr] != '\t')
        {
            temp[comparecntr] = s1[arraycntr];
            ++comparecntr;
        }
    }        
    for(arraycntr = 0; arraycntr < MAXLTR; arraycntr++)
        s1[arraycntr] = '\0';
    for(arraycntr = 0;arraycntr < MAXLTR; arraycntr++)
        s1[arraycntr] = temp[arraycntr];

}

Answer 1

This is not an assignment, but is an equality test:

s1[arraycntr] == '\t'; 

you meant:

s1[arraycntr] = '\t';

If you compile with a high warning level, the compiler may emit a message alerting you to this. The Microsoft VC compiler emits the following warning:

C:\devel\cpp\stackoverflow\main.c(32) : warning C4553: ‘==’ : operator has no effect; did you intend ‘=’?

The initial for loops only check if s1 and s2 have the same values in the same indexes, it does not check if a char in s1 exists anywhere in s2. The terminating conditions on the for loops should also be the lengths of s1 and s2, not MAXLTR:

size_t arraycntr,comparecntr;
for(comparecntr = 0; comparecntr < strlen(s2); comparecntr++)
{
    for(arraycntr = 0;arraycntr < strlen(s1) ;arraycntr++)
    {
        if(s1[arraycntr] == s2[comparecntr])
            s1[arraycntr] = `\t`;
    }
}

The next for loop should use strlen(s1) also and just assign null terminator to temp after:

comparecntr = 0;
for(arraycntr = 0; arraycntr < strlen(s1); arraycntr++)
{
    if(s1[arraycntr] != `\t`)
    {
        temp[comparecntr] = s1[arraycntr];
        ++comparecntr;
    }
}
temp[comparecntr] = '\0';

temp is not initialised anywhere, so contains random data, apart from that just entered during this for. Without a null terminator in temp, s1 will end with no null terminator also (you will probably see garbage printed afterwards). Finally, just strlen(temp) + 1 when populating s1:

for(arraycntr = 0;arraycntr < strlen(temp) + 1; arraycntr++)
    s1[arraycntr] = temp[arraycntr];

The + 1 will copy the null terminator to s1.

Minor note, instead of calling strlen() in the terminating condition of the for loops you can store this instead:

size_t chars_to_copy;
for(arraycntr = 0, chars_to_copy = strlen(temp) + 1;
    arraycntr < chars_to_copy;
    arraycntr++)
{
    s1[arraycntr] = temp[arraycntr];
}