Only present number with precision if needed - is it possible?

Question

Is there a possibility to present the same variable in different precisions?
For example, if I'm presenting an addition of two integers, it would be like:

result = 2+3;
NSLog(@"%.0f", result);

but with a division it would be like:

result = 2/3;
NSLog(@"%.1f", result);

Although presenting the π (pi) it would be like:

result = M_PI;
NSLog(@"%.19f", result); //And it would be 3.141592653589793238

Answer 1

NSNumber will do some quick-and-dirty formatting for you,

NSNumber * five = [NSNumber numberWithDouble:3+2];
NSNumber * twoThirds = [NSNumber numberWithDouble:2/3.0];
NSNumber * mPi = [NSNumber numberWithDouble:M_PI];

NSLog(@"%@", [five stringValue]);
NSLog(@"%@", [twoThirds stringValue]);
NSLog(@"%@", [mPi stringValue]);

2011-11-17 21:52:12.621 Precision[13359:903] 5
2011-11-17 21:52:12.624 Precision[13359:903] 0.6666666666666666
2011-11-17 21:52:12.625 Precision[13359:903] 3.141592653589793

but you should really use an NSNumberFormatter:

NSNumberFormatter * formatter = [[NSNumberFormatter alloc] init];

[formatter setUsesSignificantDigits:YES];

NSLog(@"%@", [formatter stringFromNumber:five]);
NSLog(@"%@", [formatter stringFromNumber:twoThirds]);

[formatter setMaximumSignificantDigits:16];
NSLog(@"%@", [formatter stringFromNumber:mPi]);

2011-11-17 21:52:12.629 Precision[13359:903] 5
2011-11-17 21:52:12.630 Precision[13359:903] 0.666667
2011-11-17 21:52:12.630 Precision[13359:903] 3.14159265358979

The string format specifiers also allow variable precision; use an asterisk instead of a digit after the decimal point:

int precision = 3;
NSLog(@"%.*f", precision, 2/3.0);