Objective -c 2.0 Chapter 6.5 Exercise

//Program to implement the following:
//Enter the expression:  number operator
// + - * / S E
// S: scanf mode
// E: end of program
/*Begins Calculations
 10 S				Set Accumulator to 10
 = 10.000000		contens of Accumulator
 2 /				Divide by 2
 = 5.000000			contents of Accumulator
 55 -				Substract 55
 = - 50.000000
 100.25 S			Set Accumulator to 100.25
 = 100.25			
 4 *				Multiply by 4
 = 401.000000		
 0 E				End of program
 = 401.000000 
 End of Calculations
 */
 
#import <Foundation/Foundation.h>
@interface Calculator : NSObject
{
	double accumulator;
}
 
-(void) setAccumulator :(double) value;
-(void) clear;
-(double) accumulator;
 
//arithmetic methods
-(double) add:(double) value;
-(double) substract:(double) value;
-(double) multiply:(double) value;
-(double) divide :(double) value;
 
@end
@implementation Calculator
 
-(void) setAccumulator:(double) value
{
	accumulator = value;
}
-(void) clear {
	accumulator = 0.0;
}
-(double) accumulator {
	return accumulator;
}
 
-(double) add: (double) value {
	accumulator += value;
	return accumulator;
}
 
-(double) substract:(double) value {
	accumulator -= value;
	return accumulator;
}
-(double) multiply:(double) value {
	accumulator *= value;
	return accumulator;
}
-(double) divide :(double) value {
	if( value == 0){
		NSLog(@"Division by 0");
		return 99999.9;
	}else {
		accumulator /= value;
		return accumulator;
	}
}
 
@end
 
int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	double value1,value2;
	char operator;
	Calculator *deskCal = [[Calculator alloc] init];
	NSLog(@"Begin Calculations");
	//set Accumulator to 10
	NSLog(@"Please Enter you expression");
	scanf("%lf %c", &value1, &operator);
	[deskCal setAccumulator:value1];
	NSLog(@"=%f", [deskCal accumulator]);
	if(operator =='S'){	
		do{
			scanf("%lf %c", &value2, &operator);
			if(operator =='+')
				[deskCal add:value2];				
			else if( operator =='-')
				[deskCal substract:value2];
			else if(operator == '*')
				[deskCal multiply:value2];
			else if(operator =='/')
				[deskCal divide:value2];
			else if(operator =='S')
				[deskCal setAccumulator:value2];	
			else if (operator =='E'){
				NSLog(@"=%f", [deskCal accumulator]);		
				NSLog(@"End of Calculations");
				break;
			}
			else 
				NSLog(@"Unknown Operator");
			NSLog(@"=%f", [deskCal accumulator]);		
		}while(operator != 'E');
	}
 
    [pool drain];
    return 0;
}