Exercise 5.8 - problems with negative numbers

[davej]

I wanted to make sure that the program would still tally the individual digits properly even if the user entered a negative integer, but after some tinkering this is the best I could come up with:

Code: (Objective-C)

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	
	int number, digit, total;
	
    NSLog (@"Enter your number.");
	scanf ("%i", &number);
	
	total = 0;
	
	while ( number < 0 )	// using the while statement to force the entered integer to positve
	{
		number *= -1;
	}
	
	while ( number != 0 )
	{
		digit =  number % 10;
		total += digit;
		number /= 10;
	}
	
	NSLog (@"The sum of the digits is %i.", total);
	
    [pool drain];
    return 0;
}

That finally worked, but it ain't pretty.  That first while statement seemed like a real roundabout way to get there.  Originally my thinking was more along these lines:

Code: (Objective-C)

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	
	int number, digit, total;

    NSLog (@"Enter your number.");
	scanf ("%i", &number);
	
	total = 0;
	
	number = (unsigned) number +0;
	
	while ( number != 0 )
	{
		digit =  number % 10;
		total += digit;
		number /= 10;
	}
	
	NSLog (@"The sum of the digits is %i.", total);
	
    [pool drain];
    return 0;
}

But that didn't work.  The line:

Code: (Objective-C)

	number = (unsigned) number +0;

doesn't seem to do the trick.  What am I missing here?  Is there a simple way to force and integer to be positive?  I feel like it has something to do with converting it to and unsigned int, right? But I can't figure out how to do it.

Thanks.

--Dave--

[skochan]

You can't do it without testing to see if it's less than zero, in which case you could just use the unary minus operator to negate it, as in

Code: (Objective-C)

number = -number;

Wait until you learn about making decisions in the next chapter and then you can fix your program.

Cheers,

Steve Kochan