Question

I’ve just solved a rather weird problem I’ve been having in an iOS Application. I need to apply a scaling factor (which I have calculated to be 64/38 ~= 1.684), to a value passed into a method.

The crux of my problem looks like this:

- (void)applyScaleTo:(int)value {

    // value := 64
    int first = value * (64/38)
    NSLog(@"First: %d", first);
    int second = (64 * value)/38;
    NSLog(@"Second: %d", second);

}

The desired value is 107, but the logs look like this:

First: 64
Second: 107

My solution is to use the second method, which is fine, but my question is, why this discrepancy? (Incidentally, if first is changed to a float, it still logs as 64.00000....)

Answer 1

In the first case you divide two integers (64 and 38) which give you an integer value back (1).
To correct that you don’t have to change the result value to a float (this will merely convert your integer result of 64 to a float), but at least one of your operants of the division.

int first = value * ( (float) 64 / 38)

This should give you 107 as a result