exercise1-21.4.c

#include <stdio.h>

#define TAB '\t'
#define TABSPACE 4
#define SPACE ' '
#define MAX 1024

/*
exercise 1-21: write a program 'entab' that replaces strings of spaces with the minimum number of tabs and blanks to achieve the same spacing. use the same number of tabs as 'detab'. When either a tab or blank would suffice to reach a tab stop, which should be given preference?
*/
int main()
{
	char oldline[MAX];
	char newline[MAX];
	int old = 0;
	int new = 0;
	int countspaces = 0;
	int tabs = 0;
	int spaces = 0;
	int is = 0;

	while (fgets(oldline, MAX, stdin))
	{
		for ( old = 0, new = 0; oldline[old] != '\0'; old++)
		{
			if (oldline[old] == ' ')
			{
				if (is == 0)
				{
					is = 1;
					++countspaces;
				}
				else if (is == 1)
				{
					++countspaces;
				}
			}
			else if ( oldline[old] != ' ' )
			{
				if ( is == 1)
				{
					tabs = (countspaces / TABSPACE);
					printf("tabs: %d", tabs);
					spaces = (countspaces % TABSPACE);
					printf("spaces: %d", spaces);
					while ( tabs > 0 )
					{
						newline[new++] = TAB;
						--tabs;
					}
					printf("tabs: %d", tabs);
					while ( spaces > 0 )
					{
						newline[new++] = SPACE;
						--spaces;
					}
					printf("spaces: %d", spaces);
					is = 0;
				}
				else
				{
					newline[new++] = oldline[old];
				}
			}
		}
		newline[new] == '\0';
		puts(newline);
	}
	return 0;
}