c_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 MAX     1000
char str[MAX];
int entab(int len);
int main()
{
        int len;
        while ((len = entab(MAX)) > 0)
                printf("%s\n", str);
        return 0;
}
int entab(int len) {
        int c, i, bl, mod, j, lc;
        i = bl = lc = 0;
        while ((c = getchar()) != EOF && c != '\n' && i < len - 1 ) {
                lc++;
                if (c == ' ') {
                        bl++;
                        if ((lc % 8) == 0) {
                                str[i++] = '\t';
                                bl = 0;
                        }
                } else {
                        if (bl) {
                                for (j = 0;j < bl;j++)
                                        str[i++] = ' ';
                                bl = 0;
                        }
                        str[i++] = c;
                }
        }
        str[i] = '\0';
        return i;
}