Question

Alright. My app has a text field and next to it are two buttons (Plus button and Equals button). When you press the “Plus” button, it takes the text inside of the textField and adds a “+” to it. Code below:

- (IBAction)plusButtonPressed:(id)sender {
    NSString *plusString = @"+";
    NSString *inputString = carbsField.text;
    NSString *outputString = [NSString stringWithFormat:@"%@%@",inputString,plusString];
    NSLog(@"%@",outputString);
    [carbsField setText:outputString];
}

I will eventually make that more intelligent so that I can’t put two pluses or whatever. Anyway, then I want the equal button to take whatever is in the textField, which should look something like: “23+54+2.2” and get the sum of those values. I believe I know how to take an Integer and make it a String, but I want to verify it:

int value = 56;
NSString *string = @"%d",value;

Well, if anyone can show me how to do this, I would be very appreciative. Thanks.

EDIT
At the moment, I have not tried anything. This is because I do not know where to start. I have an idea of what to do, but I do not know how to execute it. I believe I need to get all characters before a “+” convert them into int and then get the sum of some array of those values.

Edit #2
I now use:

- (IBAction)equalButtonPressed:(id)sender {
    NSString *inputString = carbsField.text;
    NSArray *numbers = [inputString componentsSeparatedByString:@"+"];
    int sum = 0;
    for (NSString *number in numbers) {
        sum += [number intValue];
    }
    NSString *theSum = [NSString stringWithFormat:@"%d",sum];
    NSLog(@"%@",theSum);
}

However, it won’t log anything at all. What did I do wrong?

Answer 1

It depends on how complex this is going to get. If you’re looking to implement a more complex calculator I recommend looking for an evaluator library that can do this for you.

However if all you want is to add a bunch of numbers in a list, you could do it like this:

NSString *input = @"1+2+3.5";
NSArray *numbers = [input componentsSeparatedByString:@"+"];
float sum = 0;
for (NSString *number in numbers) {
   sum += [number floatValue];
}
NSLog(@"Result: %f", sum); 

Note that this is very inflexible code and does only what you described.