ansi_c_pg34_ch01_ex21.c

/*
 * Exercise 1-21.
 * Write a program entab that replaces strings of blanks by the minimum number
 * of tabs and blanks to achieve the same spacing. Use the same tab stops as for
 * detab. When either a tab or a single blank would suffice to reach a tab stop,
 * which should be given preference?
 */

#include <stdio.h>


#define	TABSTOP	8

int
main() {
	int c;
	int offset = 0;
	int spaces = 0;

	while ((c = getchar()) != EOF) {
		if (c == ' ') {
			spaces++;
		} else {

			if (spaces) {

				if (spaces + (offset%TABSTOP) > TABSTOP) {
					spaces += (offset%TABSTOP);
				}
				offset += spaces;

				while (spaces > TABSTOP) {
					putchar('\t');
					spaces -= TABSTOP;
				}

				while (spaces) {
					spaces--;
					putchar(' ');
				}
			}

			if (c == '\n')
				offset = 0;
			else if (c == '\t')
				offset += TABSTOP - (offset%TABSTOP);
			else
				offset++;

			putchar(c);
		}
	}

	return (0);
}