CODEWITHSUNDEEP
objective-cfloating-pointrounding
nfarshchi
nfarshchi

Reputation: 1000

Rounding a float number in objective-c

I want to know if there is a simple function that I can use such this sample. I have a 

float value = 1.12345;

I want to round it with calling something like 

float value2 = [roundFloat value:value decimal:3];
NSLog(@"value2 = %f", value2);

And I get "1.123" Is there any Library or default function for that or I should write a code block for this type of calculations?

thank for your help in advance

Upvotes: 8

Views: 8908

Answers (7)

Adam Freeman
Adam Freeman

Reputation: 1278

Here is a simple way to do it:

float numberToRound = 1.12345f;
float remainder = numberToRound*1000.0f - (float)((int)(numberToRound*1000.0f));

if (remainder >= 0.5f) {
    numberToRound = (float)((int)(numberToRound*1000.0f) + 1)/1000.0f;
}
else {
    numberToRound = (float)((int)(numberToRound*1000.0f))/1000.0f;
}

For an arbitrary decimal place, substitute 1000.0f in the above code with 

float mult = powf(10.0f, decimal);

Upvotes: 0

Lil C Big Durkee
Lil C Big Durkee

Reputation: 19

//Your Number to Round (can be predefined or whatever you need it to be)
float numberToRound = 1.12345;

float min = ([ [[NSString alloc]initWithFormat:@"%.0f",numberToRound] floatValue]);
float max = min + 1;
float maxdif = max - numberToRound;
if (maxdif > .5) {
    numberToRound = min;
}else{
    numberToRound = max;
}

//numberToRound will now equal it's closest whole number (in this case, it's 1)

Upvotes: 0

Denis Kulygin
Denis Kulygin

Reputation: 323

try

#import <math.h>

float cutFloat( float number, int decimal) {
    number = number*( pow(10,decimal) );
    number = (int)number;
    number = number/( pow(10,decimal) ) ;

    return number;
}

Upvotes: -1

user207421
user207421

Reputation: 310840

Floating point numbers don't have decimal places, they have binary places. Decimal-radix numbers have decimal places. You can't round floating point numbers to specific numbers of decimal places unless you convert to a decimal radix. No routine, method, function etc., that returns a floating point value can possibly carry out this task.

Upvotes: 1

Peter M
Peter M

Reputation: 7493

Note that "Round" is not necessarily as simple a topic as you think. For example

DIY Calculator: Rounding Algorithms 101 lists 16 different methods for rounding a number.

Wikipedia:Rounding covers a lot of the same ground

And Cplusplus has source code for a bunch of Rounding Algorithms that are easy translatable to objective-c

How you want to round will depend on the context of what you are doing with for data.

And I should point out that Stack Overflow already has a plethora of other questions about rounding in objective-c

Upvotes: 0

Anne
Anne

Reputation: 27073

Using NSLog(@"%f", theFloat) always outputs six decimals, for example:

float theFloat = 1;
NSLog(@"%f",theFloat);

Output:

1.000000

In other words, you will never get 1.123 by using NSLog(@"%f", theFloat).

Cut-off after three decimals:

float theFloat = 1.23456;
float newFLoat = (int)(theFloat * 1000.0) / 1000.0;
NSLog(@"%f",newFLoat);

Output:

1.234000

Round to three decimals (using roundf() / lroundf() / ceil() / floor()):

float theFloat = 1.23456;
float newFLoat = (int)(roundf(theFloat * 1000.0)) / 1000.0;
NSLog(@"%f",newFLoat);

Output:

1.235000

Round to three decimals (dirty way):

float theFloat = 1.23456;
NSString *theString = [NSString stringWithFormat:@"%.3f", theFloat];
float newFloat = [theString floatValue];
NSLog(@"%@",theString);
NSLog(@"%f",newFloat);

Output:

1.235
1.235000

Upvotes: 7

Sulthan
Sulthan

Reputation: 130072

For printing the value use:

NSLog(@"value2 = %.3f", value2);

Rounding to 3 decimal digits before calculations doesn't really make sense because float is not a precise number. Even if you round it to 1.123, it will be something like 1.122999999998.

Rules:

  1. Usually you round up only to print the result - string formatter can handle it (see above).
  2. For precise calculations (e.g. currency), don't use floating point, use NSDecimalNumber or fixed point arithmetics.

Upvotes: 3

Related Questions