k&r exercise 1-9

[xion]

main()
{
   int c,d;

   while((c = getchar()) != EOF)
   {
       d = getchar();
       if(d == ' ')
               putchar(c);
       else{
               putchar(c);
               putchar(d);
       }
    }
}

im trying to write a program that replaces one or more blank spaces with a single blank space. this above code works if u enter 2 blank spaces some where in the string. how do i test for 3 or more blank spaces and then replace that space with a single blank space?

[WaltP]

What your code does is simply not print every other character if it is a space. In other words:
I AM HERE prints IAM HERE
and has nothing to do with consecutive spaces.

What you want to do is

Get the first character (c)
Output (c)
Start your while loop reading d
    if c != d  
        output d
    else
        if c != SPACE
             output d
    c = d
end loop

[xion]

thanks guys for responding.

walt: the code you gave me works, but im having trouble understanding the logic of the code.

at the end of the loop there is 'c = d' then at the beginning of the loop there is 'if ( c != d)'. if there is 'c = d' at the end of the loop then wouldnt it skip 'if(c != d)' statement and go to else when it looped through the second time?

[quzah]

Read the "start your loop" line.

They're talking about using something like:

while( (c = getchar()) != EOF )

This line changes the value of c each time through the loop. Thus, if c == d, then you know you've encountered a duplicate character.

Quzah.

[xion]

Originally posted by quzah
Read the "start your loop" line.

They're talking about using something like:

while( (c = getchar()) != EOF )

This line changes the value of c each time through the loop. Thus, if c == d, then you know you've encountered a duplicate character.

Quzah.

the code of the program that works is :

main()
{
	int c,d;

	c = getchar();
	putchar(c);

	while((d = getchar()) != EOF)
	{
		if (c != d)
			putchar(d);
		else {
			if (c != ' ')
				putchar(d);
		}

		c = d;
	}
}

with the help of waltp.

again i ask.

at the end of the loop there is 'c = d' then at the beginning of the loop there is 'if ( c != d)'. if there is 'c = d' at the end of the loop then wouldnt it skip 'if(c != d)' statement and go to else when it looped through the second time?

[quzah]

Asked and answered.
At the bottom of the loop, d is assigned to c.
At the top of the loop, the value of one of those two variables change, so they are no longer the same.

Quzah.

[WaltP]

Originally posted by xion
the code of the program that works is :

main()
{
	int c,d;

	c = getchar();   // Read the first (prev) character of input
	putchar(c);

	while((d = getchar()) != EOF)   // Read the next character of the input, stop if done
	{       // Check the prev and next characters
		if (c != d)
			putchar(d);
		else {
			if (c != ' ')
				putchar(d);
		}

		c = d;     // Done with prev so replace with next
	}
}

At the last line, since we are done with the character in c we replace it with the character in d. Now when we read the new d, the comparison is still with the characters adjacent in the input stream

String: trial
first comparison c='t' d='r'
replace: c='r'
second comparison c='r' d='i'
replace: c='i'
etc.

[squid]

I would do it like this.

#include <stdio.h>

int main(void)
{
	char input;

	input = getchar();
	while(input != EOF)
	{
		if(input == ' ')
		{
			while((input = getchar()) == ' ');
			putch(input);	
		}
		else
			putch(input);
		input = getchar();
	}
	
	return(0);
}

it may be a bit more complex but I really its better then using 2 different variables.

Mostly what is being done here is looping though the spaces. There is a bug in this though. Im leaving that to xion to find it

[quzah]

Originally posted by squid
I would do it like this.

	char input;

	input = getchar();
	while(input != EOF)

it may be a bit more complex but I really its better then using 2 different variables.

Mostly what is being done here is looping though the spaces. There is a bug in this though. Im leaving that to xion to find it

Well it may be complex, but it won't work. Don't write buggy code for people to fix, especially when you're already admitting it's more complex, and the only reason for doing so is because you don't feel like using two variables. Bad form. A massive four bytes isn't going to hurt anything at all in a program as simple as this. It's not wise to overly complicate your program just because you don't feel like using another integer.

Quzah.

[WaltP]

Yeah, the big bug is it removes all spaces. Serious bug if you only want to remove extra spaces.

[Hammer]

Originally posted by Salem
In that case, there are two bugs then

> while((input = getchar()) == ' ');
If this runs into EOF, you're in an infinite loop.

And for those that didn't spot the bug, go read the FAQ:
http://faq.cprogramming.com/cgi-bin/...&id=1043284351

[WaltP]

So there are (so far) 4 bugs:
1) Removes all spaces
2) Infinite loop if EOF
3) EOF is not a char
4) putch() isn't C, putchar() is (at least not in Borland 5.5)

Amazing how many misteaks can be crammed into 12 lines of C code.

[quzah]

Originally posted by WaltP
So there are (so far) 4 bugs:

4) putch() isn't C, putchar() is (at least not in Borland 5.5)

Amazing how many misteaks can be crammed into 12 lines of C code.

It's not ANSI C. It is C. And since they didn't actually add any #include lines, it's possible they are in fact including the correct header for it on their compiler.

That being said, they really should just use putchar. But assuming their compiler actually has it, and they're including the right header, it's not really an error. It's just not portable.

Quzah.

[squid]

Ok, I guess I really need to start practicing again.

[xion]

thanks for all your replies. very much appreciated =)