Objective-c calculator?

Question

Objective-C

I am writing a calculator on an iPhone (objective - c), I ran into such a problem:
Example: 2+2=4, after I want to enter a number, but it adds this number to the end of the line (I found the case 4xxx, where x is the input numbers), not as a new value.
How can it be implemented?

// Так вставляю цифры(0-9)
-(void)setNumber:(int)num{
    
    if(!isDecimal){
        displayNumber *= 10;
        displayNumber += num;
        mainLabel.text = [NSString stringWithFormat:@"%g",displayNumber];
    }
    else{
        mainLabel.text = [mainLabel.text stringByAppendingString:[NSString stringWithFormat:@"%d", num]];
    }
    displayNumber = [mainLabel.text doubleValue];
}

// При нажатие баттона, цифра добавляется в лабел
- (IBAction)num1:(id)sender {
    [self setNumber:1];
}

// При нажатие на баттон равно
- (IBAction)equals:(id)sender{
    [self operations:operation];
    mainLabel.text = [NSString stringWithFormat:@"%g",resultNumber];
    displayNumber = [mainLabel.text doubleValue];
    resultNumber = 0;
}

Answer 1

Mark with a flag that the result is received, by clicking on the number, reset this flag and clear the input line, by clicking on the operation, simply reset the flag and work further by entering 2 operands