Question

I have a situation where I have lots of different double values, for example 1.00, 0.25 and 2.50. I would like to round these doubles so that they become 1, 0.25 and 2.5; in other words I want to remove any trailing 0’s. Is there a way to do this?

At the moment I have been using %.2f, and I’m wondering if I can make use of this but adapt it in some way. Please can someone help me out?

Answer 1

As long as you’re talking only about display, this is quite easy. The format specifier you want is %g:

The double argument shall be converted in the style f or e (or in the style F or E in the case of a G conversion specifier), with the precision specifying the number of significant digits […] Trailing zeros shall be removed from the fractional portion of the result[…]

double twopointfive = 2.500;
double onepointzero = 1.0;
double pointtwofive = .25000000000;
NSLog(@"%g %f", twopointfive, twopointfive);
NSLog(@"%g %f", onepointzero, onepointzero);
NSLog(@"%g %f", pointtwofive, pointtwofive);

2011-12-06 21:27:59.180 TrailingZeroes[39506:903] 2.5 2.500000
2011-12-06 21:27:59.184 TrailingZeroes[39506:903] 1 1.000000
2011-12-06 21:27:59.185 TrailingZeroes[39506:903] 0.25 0.250000

The same format specifier can be used with an NSNumberFormatter, which will also give you some control over significant digits.

The trailing zeroes can’t be removed from the way the number is stored in memory, of course.