Answer from Paul

[zlinuk]

The Code

Code: (Objective-C)

#import <Foundation/Foundation.h>

@interface Calculator : NSObject
{
	double accumulator;
}

-(void) setAccumulator: (double) value;
-(void) clear;
-(double) accumulator;

-(void) add: (double) value;
-(void) subtract: (double) value;
-(void) multiply: (double) value;
-(void) divide: (double) value;

@end

@implementation Calculator

-(void) setAccumulator: (double) value
{
	accumulator = value;
}

-(void) clear
{
	accumulator = 0;
}

-(double) accumulator
{
	return accumulator;
}

-(void) add: (double) value
{
	accumulator += value;
}

-(void) subtract: (double) value
{
	accumulator -= value;
}

-(void) multiply: (double) value
{
	accumulator *= value;
}

-(void) divide: (double) value
{
	accumulator /= value;
}

@end

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	Calculator *deskCalc = [[Calculator alloc] init];
	
	double	number;
	char	operator;
	
	while (operator != 'E' ) {
		
		NSLog(@"Please enter a number and an operator then press return");
		scanf("%lf %c", &number, &operator);
			
			if (operator == 'E')
			break;
		
			else if (operator == 'S'){
			[deskCalc setAccumulator: number];
			NSLog(@"%g",[deskCalc accumulator]);
			}
			else {
	
				switch (operator) {
					case '+':
					[deskCalc add:number];
					NSLog(@"%g",[deskCalc accumulator]);
					break;
			
					case '-':
					[deskCalc subtract:number];
					NSLog(@"%g",[deskCalc accumulator]);
					break;
			
					case '*':
					[deskCalc multiply:number];
					NSLog(@"%g",[deskCalc accumulator]);
					break;
			
					case '/':
						if (number == 0)
							NSLog(@"Divide by zero; accumulator still = %g", [deskCalc accumulator]);
						else
							[deskCalc divide:number];
							NSLog(@"%g",[deskCalc accumulator]);
					break;
		
					default:
						NSLog(@"Unknown Operator; accumulator still = %g", [deskCalc accumulator]);
					break;
				}
			}
	}
	
    NSLog(@"%g", [deskCalc accumulator]);
	
	[deskCalc release];
    [pool drain];
    return 0;
}

The Output

Code: (Objective-C)

Loading program into debugger…
Program loaded.
run
[Switching to process 14655]
Running…
2009-09-26 17:51:32.303 Calculator[14655:a0f] Please enter a number and an operator then press return
10 S
2009-09-26 17:51:40.113 Calculator[14655:a0f] 10
2009-09-26 17:51:40.114 Calculator[14655:a0f] Please enter a number and an operator then press return
2 /
2009-09-26 17:51:49.665 Calculator[14655:a0f] 5
2009-09-26 17:51:49.666 Calculator[14655:a0f] Please enter a number and an operator then press return
55 -
2009-09-26 17:51:59.265 Calculator[14655:a0f] -50
2009-09-26 17:51:59.266 Calculator[14655:a0f] Please enter a number and an operator then press return
100.25 S
2009-09-26 17:52:13.209 Calculator[14655:a0f] 100.25
2009-09-26 17:52:13.210 Calculator[14655:a0f] Please enter a number and an operator then press return
4 *
2009-09-26 17:52:24.691 Calculator[14655:a0f] 401
2009-09-26 17:52:24.692 Calculator[14655:a0f] Please enter a number and an operator then press return
0 /
2009-09-26 17:52:39.627 Calculator[14655:a0f] Divide by zero; accumulator still = 401
2009-09-26 17:52:39.628 Calculator[14655:a0f] 401
2009-09-26 17:52:39.629 Calculator[14655:a0f] Please enter a number and an operator then press return
10 F
2009-09-26 17:52:49.340 Calculator[14655:a0f] Unknown Operator; accumulator still = 401
2009-09-26 17:52:49.341 Calculator[14655:a0f] Please enter a number and an operator then press return
0 E
2009-09-26 17:53:03.295 Calculator[14655:a0f] 401

Debugger stopped.
Program exited with status value:0.