This is my solution to exercise 1-21 of “The C Programming Language, 2nd Edition” by Kernighan and Ritchie.

#include <stdio.h>

#define TABSIZE 4     /* size of a tab stop */

/* replace strings of blanks with tabs and blanks */
int main()
{
    int c, ns = 0;

    while ((c = getchar()) != EOF)
        if (c == ' ')
            ns++;
        else {
            for (; ns >= TABSIZE; ns -= TABSIZE)
                putchar('t');
            for (; ns > 0; ns--)
                putchar(' ');
            putchar(c);
        }

    /* handle edge-case when file ends with spaces */
    for (; ns >= TABSIZE; ns -= TABSIZE)
        putchar('t');
    for (; ns > 0; ns--)
        putchar(' ');

    return 0;
}

I figured out that spaces are omitted if the input ends with spaces near end of file.

My solution involves repetition of the for loops which I know is considered a bad practice. But I think creating a seperate function to handle spaces would be too extra to an otherwise simple solution.

I tried using preprocessor macros to hide this redundancy.

#include <stdio.h>

#define TABSIZE 4     /* size of a tab stop */
#define HANDLE_SPACES(count)  { for (; ns >= TABSIZE; ns -= TABSIZE) 
                                    putchar('t'); 
                                for (; ns > 0; ns--) 
                                    putchar(' '); }

/* replace strings of blanks with tabs and blanks */
int main()
{
    int c, ns = 0;

    while ((c = getchar()) != EOF)
        if (c == ' ')
            ns++;
        else {
            HANDLE_SPACES(ns);
            putchar(c);
        }

    /* handle edge-case when file ends with spaces */
    HANDLE_SPACES(ns);

    return 0;
}

Is this a bad programming practice? What is the best option in my case?