Spaces to tabs converter

Question

I wrote a program to convert spaces to tabs. If there are 4 spaces it should convert them to tab. Please let me know how to improve it.

#include <stdio.h>
#define TABVALUE 4
int c, d, s;
int main(void) {
 c = s = d = 0;
 while ((c = getchar()) != EOF) {
 if (c == ' ') {
 s++;
 for (int j = 0; j < TABVALUE - 1; j++) {
 d = getchar();
 if (d == ' ') {
 s++;
 }
 }
 if (s == TABVALUE) {
 putchar('\t');
 s = 0;
 }
 } else {
 putchar(c);
 }
 }
 return 0;
}

• 200_success: Follow-up question

Answer 1

• Bugs

  j unconditionally loops to TABVALUE - 1. This is wrong:

  • If d happens to not be a space, it is not printed out.
  • If next d happens to be a space, it is still counted.

  Test against a b cdef. The output is a\tf.

• Silidrone: Yes, i noticed that too.But couldnt solve.Do you know how would i solve that ??
• vnp: Rewrite the inner loop as while ((c = getchar()) == ' '). Count spaces and break the loop at right time. Print either spaces or a tab. Only then print c. Care about special cases (newline for example).
• 200_success: @MuhamedCicak Is this supposed to be K&R Exercise 1-21? It's rather tricky to implement correctly. See examples 1 and 2.
• Silidrone: @200_success Thanks for the nice examples :)