K+R Exercise1_21

#include <stdio.h>

#define TABINC 8

int main()
{
    int c, nb, nt, pos;                     //nb-num blanks; nt-num tabs; pos-pos in line

    nb = nt = 0;
    for(pos=1; (c=getchar())!=EOF; ++pos)   // input a character
        if(c==' ') {                        // if its a space b4 tabstop
            if(pos%TABINC!=0)               // count it
                ++nb;                       // reset nb at tabstop
            else {
                nb=0;                       // when tabstop reached with ' ' add a tab
                ++nt;                       // count the number of tabs required
            }                               // there may be more than 1 to add
        }
        else {
            for( ; nt>0; --nt)              // note first arg missing
                putchar('\t');
            if(c=='\t')                     // if a tab has just been used reset nb
                nb=0;
            else
                for( ; nb > 0; --nb)        // if blanks stopped incrementing b4
                    putchar(' ');           // tabstop print ' ' not '\t'
                putchar(c);                 // print all chars
                if(c=='\n')                 // newline reset pos to 0
                    pos=0;
                else if(c=='\t')
                    pos = pos+(TABINC-(pos-1)%TABINC)-1;
        }

}