EXC_BAD_ACCESS error - sometimes only - iphone

Question

my app has a button that checks whether an entered value is correct.
sometimes it causes it to crash, but the strange thing is that it happens at irregular intervals (sometimes on the third iteration, sometimes the tenth, sometimes never).
i get a EXC_BAD_ACCESS error in the debugger. so it seems like something is being released when it shouldn't be. the button calls this function:
- (IBAction)checkValue:(id)sender{
int actualDifference = [firstNumberString intValue] - [secondNumberString intValue];
actualDifferenceAsString = [NSString stringWithFormat:#"%d", actualDifference];
if ([answerTextField.text isEqualToString:actualDifferenceAsString])
{
UIAlertView *correctAlert = [[UIAlertView alloc] initWithTitle:#"matches"
message:#"next value."
delegate:nil
cancelButtonTitle:#"ok"
otherButtonTitles: nil];
[correctAlert show];
[correctAlert release];
}
else
{
UIAlertView *incorrectAlert = [[UIAlertView alloc]
initWithTitle:#"does not match"
message:#"next value."
delegate:nil
cancelButtonTitle:#"ok"
otherButtonTitles: nil];
[incorrectAlert show];
[incorrectAlert release];
}
using zombies pointed to the first statement:
int actualDifference = [firstNumberString intValue] - [secondNumberString intValue];
does anyone know what the problem might be?

Answer 1

If zombies are detected in the first line, that means some other part of your program is releasing firstNumberString or secondNumberString. That's where the problem starts, but it only shows up here, when you later try to access those values. Where else do you work with those strings? Do you ever release them?
For overall safety, they should probably be assigned properties, not member variables.

Answer 2

Change it into
NSInteger actualDifference = [firstNumberString intValue] - [secondNumberString intValue]; //change int to NSInteger
NSString *actualDifferenceAsString = [NSString stringWithFormat:#"%d", actualDifference];
if ([answerTextField.text isEqualToString:actualDifferenceAsString])
{
UIAlertView *correctAlert = [[UIAlertView alloc] initWithTitle:#"matches"
message:#"next value."
delegate:nil
cancelButtonTitle:#"ok"
otherButtonTitles: nil];
[correctAlert show];
[correctAlert release];
}
else
{
UIAlertView *incorrectAlert = [[UIAlertView alloc]
initWithTitle:#"does not match"
message:#"next value."
delegate:nil
cancelButtonTitle:#"ok"
otherButtonTitles: nil];
[incorrectAlert show];
[incorrectAlert release];
}
you get this code. It worked for me...