Asterisk Histogram - Infinite Loop

**Tony92** · 08-01-2011

Hi guys. I wrote a small program where the user inputs a number and the program prints the number in asterisks. I used a for loop for this. However when I put the for loop inside a while loop to keep looping the program, it goes into an infinite loop. I just can't seem to figure out what the problem is.

Without the while loop the for loop works perfectly, printing out the asterisk(s). It's when I add the while loop that things get ugly.

Code:

#include <stdio.h>

int main(void)
{

	int number, counter;
	printf("Enter number: ");
	scanf("%d", &number);

	while (number > 0){
		for (counter = 0; counter < number; counter++){
			printf("*");
		}
	}

}

**~~CommonTater~~** · 08-01-2011

Yep, sure will... because the exit condition is never met. You need to count down your number variable until it hits 0.

**Tony92** · 08-01-2011

Would you care to explain what you mean by count down my number variable?

I can't use break statement's either. I need to exit this loop, but exit how?

**AndrewHunter** · 08-01-2011

Originally Posted by Tony92

Code:

#include <stdio.h>

int main(void)
{

	int number, counter;
	printf("Enter number: ");
	scanf("%d", &number);

	while (number > 0){
		for (counter = 0; counter < number; counter++){
			printf("*");
		}
	}

}

When does the condition in red ever evaluate to false? What is the value of number in your while loop? When does it change?

**Tony92** · 08-01-2011

Ah I see what you are saying. The printf is outside the loop so more user input cannot go through the program am I right?

When does is it ever false? When number is less than 0
What is the value of number? Whatever the user inputs
When does it change? Never I believe.

**AndrewHunter** · 08-01-2011

Originally Posted by Tony92

When does is it ever false? When number is less than 0

Actually when number is 0 or less, but you get the picture.

Originally Posted by Tony92

What is the value of number? Whatever the user inputs

ok.

Originally Posted by Tony92

When does it change? Never I believe.

So if number never changes in your while loop why do you expect your while loop to end? Note you never ask for another number to be inputted in your while loop.

**Tony92** · 08-01-2011

Yeah I figured that out. The thing is if I put my input statements inside my while loop, the first time the program runs it won't run properly. A Do-While loop will work but the outline says I should use a pre-test loop.

**anduril462** · 08-01-2011

So ask the user once before the loop, then again as the last thing inside the loop.

**Tony92** · 08-01-2011

There we go I fixed it, tell me what you think.

Code:

#include <stdio.h>

int main(void)
{

	int number = 1, counter;
	
	
	while (number > 0){
        printf("Enter a number: ");
	    scanf("%d", &number);
		for (counter = 0; counter < number; counter++){
			printf("*");
		}

	}


}

**anduril462** · 08-01-2011

Yep, that works too. Hopefully the instructions say not to use a do-while loop so you can see just how stupid it is to do something like this with a pre-test loop. This is exactly when you should use a do-while.

**Matticus** · 08-01-2011

Seems like you got it. I would also recommend that you return an integer at the end of "main()" - typically zero for normal program termination.

**Tony92** · 08-01-2011

Yeah it was really irritating me, it specifically said to use a pre-test loop and I think you're right it's to show when exactly is the time to use a do-while. Thanks for your help guys.

**Tony92** · 08-01-2011

Originally Posted by Matticus

Seems like you got it. I would also recommend that you return an integer at the end of "main()" - typically zero for normal program termination.

Oh yes I almost forgot about that.

**AndrewHunter** · 08-01-2011

1. You define main as returning an int correctly, however you forgot to actually return one, e.g. return(0);

Other than that, good work. Just keep in mind the way you have your loop setup if the user enters zero to quit your program will still evaluate the for-loop before exiting. Not a big problem for this case however loop logic can become tiresome. For example you could have done:

Code:

#include <stdio.h>

int main(void)
{

	int number, counter;
	
	printf("Enter a number: ");
	scanf("%d", &number);
	
	while (number > 0){
		for (counter = 0; counter < number; counter++){
			printf("*");
		}
		printf("Enter a number: ");
	             scanf("%d", &number);
	}

	return (0);
}

EDIT: Holy rapid fire posts while I was typing mine up.

**Tony92** · 08-01-2011

That is true.

One question the return 0; why did you add brackets around the 0? I was taught that it was only return 0; and not return (0);

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