#include <stdio.h>
#include <stdlib.h>
#define TABSTOP 4

void detab(int tabstop);
int fill(int indent, int tabstop);

/* detab input, takes one optional argument for tabstop width */
int main(int argc, char *argv[])
{
    int tabstop;

    if (argc < 2 || !(tabstop = atoi(argv[1])))
        detab(TABSTOP);
    else
        detab(tabstop);

    return 0;
}


/* detabs input with spaces, tab stop width is 'tabstop' */
void detab(int tabstop)
{
    int c, indent = 0; /* indent starts at 0 */

    while ((c = getchar()) != EOF)
        if (c == '\t')
            indent = fill(indent, tabstop);
        else {
            putchar(c);
            indent = (c == '\n') ? 0 : indent + 1;
        }
}

/* fills output with spaces from indent to next tabstop */
/* returns new indent */
int fill(int indent, int tabstop)
{
    int w = tabstop - indent % tabstop;
    
    for (; w > 0; --w) {
        putchar(' ');
        ++indent;
    }
         
    return indent;
}