Question

For some reason, my following line of code is returning a 0.

int bac = [food.text intValue] * 12 * 0.042 * 5.14 / [weight.text intValue] * 0.73;

I can’t seem to figure out why. food and weight are both UITextFields. Any help would be very much appreciated.

Does it have anything to do with the int needing to be a float? or a double?

Here is my entire method:

-(IBAction) calcBac {

    float bac = [food.text floatValue] * 12 * 0.042 * 5.14 / [weight.text floatValue] * 0.73;
    NSString *msg = [[NSString alloc] initWithFormat: @"Results: You're BAC is %d", bac];
    result.text = msg;
    [msg release];

}

Answer 1

A couple things:

• Make sure your data types are consistent. It is best to use float, so that you don’t lose fractional parts in the computation, but you can’t turn around and try to display it with an int formatter (%d).

So, to clean up your example:

float bac = [food.text floatValue] * 12 * 0.042 * 5.14 / [weight.text floatValue] * 0.73;
NSString *msg = [[NSString alloc] initWithFormat: @"Results: You're BAC is %.2f", bac];

The formatter of %.2f says to display the float with 2 decimal places.

• Order of operations. If the value is still incorrect, realize that (as written) each operation will be executed in order. If you need to group operations (like you really wanted to divide the entire first part by the entire second part), then add parentheses for grouping.

In other words, possibly what you really meant was (although I’m not sure):

float bac = ([food.text floatValue] * 12 * 0.042 * 5.14) / ([weight.text floatValue] * 0.73);
NSString *msg = [[NSString alloc] initWithFormat: @"Results: You're BAC is %.2f", bac];

Without any grouping, running the numbers on a calculator for the 5/160 example you gave, I get a result of ~0.059. If that’s not the output you are looking for, you may be missing some grouping symbols.

HTH