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Full Discussion: Text stream K&R exercises
Operating Systems OS X (Apple) Text stream K&R exercises Post 302387553 by Jammer Six on Sunday 17th of January 2010 05:17:01 AM
Old 01-17-2010
Thank you, Franklin.

I took your suggestion of a flag, and after wrestling with it for a few hours, came up with this:

Code:
/*
 *  copy.c
 *  
 *	Exercise 1-9. Write a program to copy it's input to it's output,
 *	replacing each string of one or more blanks by a single blank.
 */


#include	<stdio.h>

main() {
	
	int	c;	// The current character
	int	blank;	// flag that is set when we get the first blank space
	
	c = blank = 0;
	
	printf("\n\n");	// just so I can read the output
	
	while ((c = getchar()) != EOF) {
		
		if (c != ' ')		{	// if c is not holding a blank space
			putchar(c);			// print it
		}						// end if
			else if (!blank) {	// c is a blank space, if it's the first blank space
				blank = 1;		// set blank to show we already have the first blank
				putchar(c);		// printed
			}					// end else if
		
			else	{			// we're in a string of two or more blanks
				
				while ((c = getchar()) == ' ') {
					
/* as long as we're in the string of blanks					
 do nothing, kick out when we get the first non-blank	*/
					
					;	// The do nothing command		
				}		// end while
				
/* c now holds the first character after the string of blanks, 
reset blank, print one blank, and print the character */
				
				blank = 0
				printf(" ");
				putchar(c);
				
			}					// end final else
	}							// end main while loop
	
	printf("\n\n");				// just so I can read the output
	
}								// end main

It works, and it works reliably, but there's one thing I don't like about it.

If I'm following it correctly, (and I'm pretty sure I am) the flag blank carries a 1 as soon as a single blank is encountered.

That is, if you ran it on this sentence, the space between "That" and "is" would set blank to one, and it would be one until it was re-set, and it wouldn't be re-set until the word "if".

So it would work, it wold do its assigned task correctly, and the code would use the first else if when it didn't have a blank set, and the second else if when it did.

So my only gripe is that the flag blank isn't reliable-- it does not show the truth about whether the first blank has been encountered at all times.

On the other hand, when I swore at it, I woke my wife up, so I think I'll put it away for tonight.
 

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LEARN ABOUT PLAN9

iswblank

ISWBLANK(3)						     Linux Programmer's Manual						       ISWBLANK(3)

NAME

       iswblank - test for whitespace wide character

SYNOPSIS

       #include <wctype.h>

       int iswblank(wint_t wc);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       iswblank():
	      _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION

       The  iswblank() function is the wide-character equivalent of the isblank(3) function.  It tests whether wc is a wide character belonging to
       the wide-character class "blank".

       The wide-character class "blank" is a subclass of the wide-character class "space".

       Being a subclass of the wide-character class "space", the wide-character class "blank" is disjoint from the  wide-character  class  "graph"
       and therefore also disjoint from its subclasses "alnum", "alpha", "upper", "lower", "digit", "xdigit", "punct".

       The wide-character class "blank" always contains at least the space character and the control character '	'.

RETURN VALUE

       The  iswblank()	function  returns  nonzero if wc is a wide character belonging to the wide-character class "blank".  Otherwise, it returns
       zero.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +-----------+---------------+----------------+
       |Interface  | Attribute	   | Value	    |
       +-----------+---------------+----------------+
       |iswblank() | Thread safety | MT-Safe locale |
       +-----------+---------------+----------------+
CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       The behavior of iswblank() depends on the LC_CTYPE category of the current locale.

SEE ALSO

       isblank(3), iswctype(3)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

GNU
								    2016-03-15							       ISWBLANK(3)
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