Question

Am getting two errors in my model implementation file, which I have commented out. Can you explain what’s wrong and how to fix it?

Thank you.

---

CalculatorBrain.m

#import "CalculatorBrain.h"

@interface CalculatorBrain()
@property (nonatomic, strong)NSMutableArray *operandStack; 

@end

@implementation CalculatorBrain

@synthesize operandStack = _operandStack;

- (NSMutableArray *)operandStack
{
     if (!_operandStack) {
    _operandStack = [[NSMutableArray alloc]init];
    }
    return _operandStack;
}

 - (void)setOperandStack:(NSMutableArray *)anArray
{
    _operandStack = anArray;
}

- (void)pushOperand:(double)operand
{
    [NSNumber *operandObject = [NSNumber numberWithDouble:operand]; // Expected     identifier
     [self.operandStack addObject:operandObject]; /* Use of undeclared identifier     'operandObject' */
}

- (double)popOperand
      {
         NSNumber *operandObject = [self.operandStack lastObject];
         return [operandObject doubleValue];
      }

 - (double)performOperation:(NSString *)operation
{
    double result = 0;

    if ([operation isEqualToString:@"+"]) {
        result = [self popOperand] + [self popOperand];
    } else if ([@"*" isEqualToString:operation]) {
        result = [self popOperand] * [self popOperand];
    } else if ([operation isEqualToString:"-"]) {
        double subtrahend = [self popOperand];
        result = [self popOperand] - subtrahend;
    } else if ([operation isEqualToString:@"/"]) {
        double divisor = [self popOperand];
        if (divisor) result = [self popOperand] / divisor;
    }

     [self pushOperand:result];

     return result;
}


@end

Answer 1

You have a stray [:

[NSNumber *operandObject = [NSNumber numberWithDouble:operand]; 
^