Question

I know that there are many different questions about this sort of topic on SO already, but I couldn’t find a way to tailor them all to my specific needs.

What I have is a floating point number that gets sent to me through the network that I need to convert and graph out to the screen. The numbers can range from 5.2, 285.159, 294729172.258, -10734.112, etc. What I would like to do is get the value used to round from one digit below the most significant digit.

Example:

5.2 = 5
285.159 = 300
294729172.258 = 300000000
-10734.112 = -11000

Any advice that can be used to help guide me would be greatly appreciated.

Answer 1

Here’s my solution:

int roundMostSignificant(float input)
{
    NSNumber *number = [NSNumber numberWithFloat:input];
    static NSNumberFormatter *formatter = nil;

    if (!formatter)
    {
        formatter = [NSNumberFormatter new];
        [formatter setMinimumSignificantDigits:1];
        [formatter setMaximumSignificantDigits:1];
        [formatter setUsesSignificantDigits:YES];
    }

    return [[formatter numberFromString:[formatter stringFromNumber:number]] intValue];
}

Yes, this uses objects, but I think that this will be your best bet in the long run, as it handles rounding, parsing, etc. for you.