Exercise 6.2

[clouded]

Here's my solution, not the prettiest, but it works:

Code: (Objective-C)

// Chapter 6 Exercise 2.
// Program 6.8A displays the value in the accumulator even 
// if an invalid operator is entered or division by zero is 
// attempted. Fix that problem.

// Program 6.8A
// Program to evaluate simple expressions of the form 
// value operator value

#import <Foundation/Foundation.h>

@interface Calculator: NSObject
-(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 
{
    double accumulator; 
}
-(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, char * argv[]) {
    
    @autoreleasepool {
        
        double value1, value2;
        char operator;
        Calculator *deskCalc = [[Calculator alloc] init];
        
        NSLog (@"Type in your expression.");
        scanf ("%lf %c %lf", &value1, &operator, &value2);
        
        [deskCalc setAccumulator: value1];
        if ( operator == '+' ) 
            [deskCalc add: value2];
        else if ( operator == '-' ) 
            [deskCalc subtract: value2];
        else if ( operator == '*' ) 
            [deskCalc multiply: value2];
        else if ( operator == '/' ) 
            if ( value2 == 0 )
                NSLog (@"Division by zero."); 
            else
                [deskCalc divide: value2]; 
            else
                NSLog (@"%c = unknown operator.", operator); // Tell user what is wrong
        
        if ( value2 != 0 )
            if ( operator == '+')
                NSLog (@"%.2f", [deskCalc accumulator]);
            else if ( operator == '-')
                NSLog (@"%.2f", [deskCalc accumulator]);
            else if ( operator == '*')
                NSLog (@"%.2f", [deskCalc accumulator]);
            else if ( operator == '/')
                NSLog (@"%.2f", [deskCalc accumulator]);
    }
    return 0;
}

Output:

Type in your expression.
1/2
0.50

Type in your expression.
1 * 2
2.00

Type in your expression.
1 + 2
3.00

Type in your expression.
1 - 2
-1.00

Type in your expression.
1 q 2
q = unknown operator.

Type in your expression.
1 x 2
x = unknown operator.

Type in your expression.
1 > 2
> = unknown operator.

[stuartjj]

Clouded,
I believe that in your program if you multiply, add, or subtract by 0, the accumulator result is not printed.