Learning C

[Alexander]

Ok, I'm kind of confused. I swore I understood what I was doing a second ago. xD
I'm trying to learn C and failing apparently. My tutorial gave me this assignment:

Assignment: Write a program that repeatedly accepts user input and then prints the numbers between 0 and the entered number. If the user enters a number less than or equal to zero, the program will exit.

So, I thought that it would be easy enough. So I write some probably atrocious code.

#include <stdio.h>

int main(void){

	int x, z = 0; //variables
	scanf("&#37;d",x); //user input

	if(x>0){ //check user input
	
		int y;
		for(y=1;y<=x;y++){ //loop to add all integers between 0 and x together
			z += y;
		}

		printf("%d\n",z); //print result
		main(); //restart
	}

	return 0; //end
}

After compiling, I run and it gives me this:
20776 [main] a 2268 _cygtls::handle_exceptions: Error while dumping state (probably corrupted stack)
Segmentation fault (core dumped)

Now I really have no idea what I'm doing. Can anyone give me pointers? -.-;

[Adak]

You need a while loop to enclose the scanf() line. As is, you have no "until" in there.

And don't forget to synch up your scanf() with a getchar() to get past the newline char when you hit the enter key.

[Dino]

Go to this web site and read about scanf() and how to use it.

http://www.cppreference.com/stdio/index.html

[master5001]

Also, and more importantly, you need to change your parameters around on scanf() too.

Example

scanf("%d",&x);

Usually people are all over these kinds of errors... It must be a day where people have those one things that I almost never have... what are they called... Oh yeah, a social life.

[MK27]

scanf("%d",&x);

not scanf("%d,x) but don't ask me why. I would just call it a reference.

Also, you should move main() down two lines (past } and before return) if you want the loop to work.

[master5001]

Silly me, I didn't even explain to you what that & means or why you are putting it there. My deepest apologies.

The & thingy denotes when you are wanting to take the memory address of a variable. In this case you need the memory address of x. Why do you need that? Because if you give scanf() the address of x, it can write to that specific place in memory. Otherwise if you just pass in x, it will interpret the value which x holds (which since you didn't initialize x, its value is going to be undefined) as a memory address.

So if x initialized to lets say... -351. It will try to write to the whatever is the 0xFFFFFEA1 (or 0xFFFFFFFFFFFFFEA1 on a 64-bit platform) memory address.

Of course that is a crazy memory address that your program doesn't have the right to be writing to, thus there may be a segment fault or stack corruption depending on what exactly was attempted to be written to. Is that helpful?

[master5001]

Oh whoa... I didn't even see the main() thing until MK27 mentioned it. Why in the hell are you recursing main()? I am not liking your freakish voodoo program you are trying to write here...

[cpjust]

main(); //restart

In addition to the problems mentioned above with scanf(), calling the main() function in your program is illegal. Take it out and save yourself a lot of grief!

[Alexander]

Gah! I'm retarded. I forgot the address part. Sorry. ^^; Thanks for that. And what do you mean by having to enclose the scanf() in a while loop? o.o I didn't know I had to do that. And I want the loop to only work if the user has entered a number larger then 0.

[Alexander]

main(); //restart

Calling the main() function in your program is illegal. Take it out and save yourself a lot of grief!

Yeah, but then it stops. How should I make the program restart again preferably?

[cpjust]

Move all the code that's in your main() function into another function, then you can call that other function as much as you like.

[Alexander]

You need a while loop to enclose the scanf() line. As is, you have no "until" in there.

And don't forget to synch up your scanf() with a getchar() to get past the newline char when you hit the enter key.

Oh! Now I get what you mean!

#include <stdio.h>

int main(void){

	int x, z = 0; //variables

	while(x>0){ //check user input
                scanf("&#37;d",&x); //user input
		int y;
		for(y=1;y<=x;y++){ //loop to add all integers between 0 and x together
			z += y;
		}

		printf("%d\n",z); //print result
	}

	return 0; //end
}

But I don't get what you mean by the getchar(), unfortunately, I have no idea how to use that yet.

[Alexander]

Move all the code that's in your main() function into another function, then you can call that other function as much as you like.

Hmm, yeah. I didn't want to do that, I know how to do functions, but my tutorial hadn't gotten to them yet, so I thought I'd do it with out that and do it with what they have taught me so far.

[cpjust]

Hmm, yeah. I didn't want to do that, I know how to do functions, but my tutorial hadn't gotten to them yet, so I thought I'd do it with out that and do it with what they have taught me so far.

Then use a loop, or if you're feeling particularly naughty, you could always try a goto statement.

[Alexander]

Then use a loop, or if you're feeling particularly naughty, you could always try a goto statement.

Oooh, I like the goto statement. Is there a drawback to it though?