Question

Hi i am trying to get an integer value from a NSMutableArray I called programStack which holds all the numbers. This method is an undo method so when I hit undo it erases the last item on the stack and returns the previous option. When i try to get the number the method undoVariable has the right value for string when it is returned but then after when it is displayed I get the wrong value. An example is having 2, 3 on the array. I erase 3 and string shows 2 in UndoVariable and then when I use self.display.text to display it displays 1.57539e-302. Could this be the pointer address? Here is the code.

- (IBAction)undoPressed {

NSString* string = self.display.text;

if(userIsInTheMiddleOfEnteringANumber){
    if([self.display.text length])
        string = [string substringToIndex:([string length]-1)];

} else {
    string = [NSString stringWithFormat:@"%g",[self.brain undoVariable]];
    NSLog(@"string is %@", string);
}

    self.display.text = string;
}

-(NSString*) undoVariable{

if(self.programStack)
[self.programStack removeLastObject];
    if(self.programStack){
        NSString* string = @"";
        string = [string stringByAppendingString: [self.programStack lastObject]];
        NSLog(@"string = %@", string);
        NSLog(@"self.display.text = %@", [self.programStack lastObject]);
        return string;
}

Answer 1

Your %g format says to treat the given value as a floating point number but undoVariable says it returns a NSString. If you really wanted to format it, you’d need %@. However, it’s much simpler to just use the string rather than reformatting it, as in: string = [self.brain undoVariable];.