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Full Discussion: Text stream K&R exercises
Operating Systems OS X (Apple) Text stream K&R exercises Post 302386899 by pludi on Thursday 14th of January 2010 03:56:36 AM
Old 01-14-2010
Quote:
Originally Posted by Jammer Six
Code:
// Test.c

#include <stdio.h>

	//Verify that the expression "getchar() != EOF" is 0 or 1.
	//Exercise 1-6 on page 17.

main()	{
	
	int	c;
	
	c = getchar();
	
	while (c != EOF) {
		while (c != 1) { 
			while (c != 0) {// You only get here if c is not 1.
				printf("EOF is not 1 or 0.");	//c is not 1 or zero.
			}	//end while test for zero
		}	// end while test for 1
		
		printf("\nThe value passed, because EOF is ");
		printf("%d\n",	c);
	}
}

When I run it, it doesn't appear to do anything, until I type something. Then it enters an endless loop, and doesn't exit unless I close the Terminal window.

I don't see how I'm creating a loop.
You've got 3 while-loops in there, each one checking the value of the variable c, which is never changing. So as soon as you enter any character, enters the outermost while loop. Since it's pretty unlikely to enter the characters with the ASCII codes 0 or 1 via the keyboard, the two inner loops will run until killed (by Ctrl+C or by closing the Terminal).
Quote:
Originally Posted by Jammer Six
I also don't see (in the K&R book) how to obtain a text stream other than from the keyboard.

Any help will be welcome.
There are 2 possibilities: you can do a redirection in your terminal (eg
Code:
cat /some/file | ./a.out

), or by opening a file using open/fopen. If I remember correctly, those are introduced later in the book.
Quote:
Originally Posted by Jammer Six
This code is a different type of problem:

Code:
// count.c
#include	<stdio.h>

// count characters in input, page 18 of C book, version 1

main()	{
	
	long	nc;
	
	nc = 0;
	
	while (getchar()!=EOF) {
		++nc;
		printf("%ld\n",	nc);
	}	// end of while
}	// end of main

This code is straight out of the K&R book. What it does is nothing, until you type something. Then it generates a random number of numbers. It also doesn't quit unless you quit the Terminal window.
getchar() is a so-called blocking function. That means, it will sit and block the calling program until it can return something, in this case a character read from stdin. While it gets characters that don't signal an End-Of-File, it will count up.

EOF is usually input by the keyboard combination Ctrl+D on Unix-like systems (including BSD-descended MacOS X)
 

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