Calculator divide by zero - ios

Question

I created a simple calculator. Everything works great; however, if I divide by zero, I would like to show an error message. I know how to do alert popups, but I don't know how to implement it so it comes up when I divide by zero. Here is a snipped of my calculator code:
- (IBAction)buttonOperationPressed:(id)sender {
if (currentOperation == 0) result = currentNumber;
else {
switch (currentOperation) {
case 1:
result = result + currentNumber;
break;
case 2:
result = result - currentNumber;
break;
case 3:
result = result * currentNumber;
break;
case 4:
result = result / currentNumber;
break;
case 5:
currentOperation = 0;
break;
default:
break;
}
}
currentNumber = 0;
CalcDisplay.text = [NSString stringWithFormat:#"%g",result];
if ([sender tag] == 0) result = 0;
currentOperation = [sender tag];
userInTheMiddleOfEnteringDecimal = NO;

Answer 1

You can just add a test prior to doing the division e.g. change:
case 4:
result = result / currentNumber;
break;
to:
case 4:
if (currentNumber == 0)
// ... do alert here ...
else
result = result / currentNumber;
break;

Answer 2

You have to check if the second division operand is zero, and if yes, then print an error message. Don't forget, that you can't just compare double or something with ==, you have to use presicion, like this:
case 4:
if(ABS(currentNumber) < 1e-12) // most probably its zero
// your message
return;

Answer 3

- (IBAction)buttonOperationPressed:(id)sender {
if (currentOperation == 0) result = currentNumber;
else {
switch (currentOperation) {
case 1:
result = result + currentNumber;
break;
case 2:
result = result - currentNumber;
break;
case 3:
result = result * currentNumber;
break;
case 4:
if(currentNumber == 0){
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Title" message:#"Message" delegate:nil cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[alert show];
}else{
result = result / currentNumber;
}
break;
case 5:
currentOperation = 0;
break;
default:
break;
}
}
currentNumber = 0;
CalcDisplay.text = [NSString stringWithFormat:#"%g",result];
if ([sender tag] == 0) result = 0;
currentOperation = [sender tag];
userInTheMiddleOfEnteringDecimal = NO;
Please try this code, I have copied an pasted the code you have given and added some necessary lines to it which i felt would solve your issue.