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

void entab(int tabstop);

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

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

    return 0;
}


/* entabs input with spaces, tab stop width is 'tabstop' */
void entab(int tabstop)
{
    int c, indent; /* indent starts at 1 */
    int bn = 0; /* current number of blanks */

    for (indent = 1; (c = getchar()) != EOF; ++indent)
        if (c == ' ') {
            if (indent % tabstop || bn == 0)
                /* dont entab single spaces */
                ++bn;
            else {
                bn = 0;
                putchar('\t');
            } 
        } else {
            for(; bn > 0; --bn)
                putchar(' ');
            putchar(c);
            if (c == '\n')
                indent = 0;
        }
}