Rounding numbers in Objective-C

问题

I'm trying to do some number rounding and conversion to a string to enhance the output in an Objective-C program.

I have a float value that I'd like to round to the nearest .5 and then use it to set the text on a label.

For example:

1.4 would be a string of: 1.5

1.2 would be a string of: 1

0.2 would be a string of: 0

I've spent a while looking on Google for an answer but, being a noob with Objective-C, I'm not sure what to search for! So, I'd really appreciate a pointer in the right direction!

Thanks, Ash

回答1:

Thanks for the pointers everyone, I've managed to come up with a solution:

float roundedValue = round(2.0f * number) / 2.0f;
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setMaximumFractionDigits:1];
[formatter setRoundingMode: NSNumberFormatterRoundDown];

NSString *numberString = [formatter stringFromNumber:[NSNumber numberWithFloat:roundedValue]];
[formatter release];

The above works for the test cases I threw at it, but if anyone knows a better way to do this I'd be interested to hear it!

回答2:

float floatVal = 1.23456;

Rounding

int roundedVal = lroundf(floatVal); 

NSLog(@"%d",roundedVal);

Rounding Up

int roundedUpVal = ceil(floatVal); 

NSLog(@"%d",roundedUpVal);

Rounding Down

int roundedDownVal = floor(floatVal);

NSLog(@"%d",roundedDownVal);

回答3:

NSString *numberString = [NSString stringWithFormat:@"%f", round(2.0f * number) / 2.0f];

回答4:

Use lroundf() to round a float to integer and then convert the integer to a string.

回答5:

NSString *numberString = [NSString stringWithFormat:@"%d",lroundf(number)];

回答6:

I'd recommend looking into using NSNumberFormatter.

回答7:

a simple way:

float theFloat = 1.23456;
int rounded = roundf(theFloat); NSLog(@"%d",rounded);
int roundedUp = ceil(theFloat); NSLog(@"%d",roundedUp);
int roundedDown = floor(theFloat); NSLog(@"%d",roundedDown);
// Note: int can be replaced by float

回答8:

NSString *intNumberString = [NSString stringWithFormat:@"%d", (int)floatNumber];

回答9:

Following Technique worked for me in a financial application.

 NSString *dd=[NSString stringWithFormat:@"%0.2f",monthlyPaymentCalculated];

        monthlyPaymentCalculated=[dd doubleValue];

self.monthlyPaymentCritical=monthlyPaymentCalculated;

what is did is first is rounded it with %0.2f and stored it in NSString then i simply converted it again into double and result was good for my calculation.

回答10:

I needed to be able to round to a specific digit (not necessarily to whole integers). I made a NSNumber category (based off Ash's answer) and added the following method to it:

- (NSString *)stringByRounding:(NSNumberFormatterRoundingMode)roundingMode
      toPositionRightOfDecimal:(NSUInteger)position
{
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    [formatter setMaximumFractionDigits:position];
    [formatter setRoundingMode:roundingMode];
    NSString *numberString = [formatter stringFromNumber:self];
    return numberString;
}

Which allows me to use it like so:

[aNumber stringByRounding:NSNumberFormatterRoundUp toPositionRightOfDecimal:2];

I can use it to round to integers by passing in 0 as the second parameter:

[aNumber stringByRounding:NSNumberFormatterRoundPlain toPositionRightOfDecimal:0];

回答11:

With these functions you can round to any value.. If you use p=2, you get even numbers.

float RoundTo(float x, float p)
{
  float y = 1/p;
  return int((x+(1/(y+y)))*y)/y;
}

float RoundUp(float x, float p)
{
  float y = 1/p;
  return int((x+(1/y))*y)/y;
}

float RoundDown(float x, float p)
{
  float y = 1/p;
  return int(x*y)/y;
}

来源：https://stackoverflow.com/questions/752817/rounding-numbers-in-objective-c