Thread: K&R detab

Hello all! This is my first thread! I actually signed up to post, because i saw that several people here on the forum have asked about this exercise in the past. Basically, the task is to replace tabs with spaces, ensuring that the number of spaces is appropriate to get you to the next tab stop (i.e. if you were only 4 spaces away from a tab stop, don't replace the tab with 8 spaces).

Anyway, i'm not posting because i can't figure it out. I'm posting because i did figure it out, and i'm not sure if my code is good enough. I think all of the solutions i've seen have included character arrays, and many have included multiple functions. I realize the text says "these exercises suggest programs of somewhat greater complexity than the ones earlie in this chapter," but it seemed like a very straightfortward task.

Have i oversimplified or something?

Code:

#include <stdio.h>

#define TAB_STOP 8

int main()
 {
  int c, i;

  c=0;

  for (i=TAB_STOP; (c=getchar()) != EOF; --i)
   {
    if (i<=0)
      i=TAB_STOP;

    if (c=='\n')
      i=TAB_STOP+1;

    if (c=='\t')
      while (i>0)
       {
        printf(" ");
        --i;
       }
    else
      putchar(c);
   }

  return 0;
 }

Both loops are decrementing i.

The outer loop, which is pulling input, decrements i in its declaration statement. There's an if statement inside that resets i to the defined tab length when it hits 0. This way, the count just keeps resetting itself until it hits a tab, and the value of i at that point is the number of spaces needed.

The while loop takes that value and decrements as well, printing spaces until the counter hits 0. At this point, the outer loop picks back up, and the leading if statement resets to 8 in case there are consecutive tabs

My initial question wasn't about finding a valid solution; it was more about whether my approach in solving the problem looks good enough. I am learning C now and want to be sure i'm forming good habits for later.

I wasn't sure if i should split the program into a couple of functions (as the textbook seems to suggest) or if it's fine as-is since it's so short. I guess i could have done something like this:

Code:

    if (c=='\t')
      i=addspaces(i);
    else
      putchar(c);

...but it seemed silly to me to make a new function that only holds a single loop.

but it seemed silly to me to make a new function that only holds a single loop.

Nothing silly about that.

To develop the program more, make it so the user can enter a tab size from the command line.
If they run it without giving a size, then use the default of 8.
Deal with the command line in main and pass off the tabsize to a separate detab function.