pra1-21_Solution.c

#include <stdio.h>

#define MAXLINE 1000 /* max input line size */
#define TAB2SPACE 4 /* 4 spaces to a tab */

char line[MAXLINE]; /*current input line*/

int getline(void);  /* taken from the KnR book. */


int
main()
{
  int i,t;
  int spacecount,len;

  while (( len = getline()) > 0 )
    {
      spacecount = 0;
      for( i=0; i < len; i++)
	{
	  if(line[i] == ' ')
	    spacecount++; /* increment counter for each space */
	  if(line[i] != ' ')
	    spacecount = 0; /* reset counter */
	  if(spacecount == TAB2SPACE) /* Now we have enough spaces
				      ** to replace them with a tab
				      */
	    {
	      /* Because we are removing 4 spaces and
	      ** replacing them with 1 tab we move back 
	      ** three chars and replace the ' ' with a \t
	      */
	      i -= 3; /* same as "i = i - 3" */
	      len -= 3;
	      line[i] = '\t';
	      /* Now move all the char's to the right into the
	      ** places we have removed.
	      */
	      for(t=i+1;t<len;t++)
		line[t]=line[t+3];
	      /* Now set the counter back to zero and move the 
	      ** end of line back 3 spaces
	      */
	      spacecount = 0;
	      line[len] = '\0'; 
	    }
	}
      printf("%s", line);
    }
  return 0;
}


/* getline: specialized version */
int getline(void)
{
  int c, i;
  extern char line[];
  
  for ( i=0;i<MAXLINE-1 && ( c=getchar()) != EOF && c != '\n'; ++i)
    line[i] = c;
  if(c == '\n') 
    {
      line[i] = c;
      ++i;
    }
  line[i] = '\0';
  return i;

}