DaniWeb Forum Index > Software Development > C++

Rounding

Please support our C++ advertiser: Programming Forums - DaniWeb Sister Site

•

Join Date: Sep 2008

Posts: 3

Reputation: brent.lozano001 is an unknown quantity at this point

Solved Threads: 0

brent.lozano001 brent.lozano001 is offline

Offline

Newbie Poster

Re: C++ if statement help

Sep 16th, 2008

im trying to learn how to make a if/then statement that will take a number, possibly with a decimal and round it to the nearest integer. Like so..

if 3.4 is the number, then the final would be 3 not 3.4

how would i do so?

•

Join Date: Mar 2008

Posts: 1,497

Reputation: William Hemsworth has much to be proud of

Solved Threads: 123

William Hemsworth William Hemsworth is offline

Offline

Nearly a Posting Virtuoso

Re: Rounding

Sep 16th, 2008

Rounding a number to the nearest whole number is one of the easiest things you can do in C++

there isn't even any need for an if/else statement, take this as an example.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
float decimal = 3.4f;
int rounded = int(decimal + 0.5f); // 3
float decimal = 3.4f;
int rounded = int(decimal + 0.5f); // 3

Hope this helps.

Last edited by William Hemsworth; Sep 16th, 2008 at 5:40 pm.

•

Join Date: Sep 2008

Posts: 2

Reputation: erabyss is an unknown quantity at this point

Solved Threads: 0

erabyss

Offline

Newbie Poster

Re: Rounding

Sep 16th, 2008

Yes it does. Thank you.

I wasnt the one who posted the question, but I am workin on a program that has a sim problem. Its a calculater that that works out the ultimate return on a purchase. I am writing it for an MMORPG I play.

This was a big help, thnk you. =]

•

Join Date: Jul 2008

Posts: 2,001

Reputation: ArkM has much to be proud of

Solved Threads: 343

ArkM

Offline

Postaholic

Re: Rounding

Sep 16th, 2008

1. Regrettably, for negative numbers williamhemsworth's solution does not work (moreover, gives wrong result - for example, it yields 0 for -0.9 but nearest integer value for -0.9 is -1). Right solution:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <cmath>
...
double round(double x) {
    bool negative = false;
    if (x < 0.0) {
        x = -x;
        negative = true;
    }
    x = std::floor(x+0.5);
    return negative? -x: x;
}
#include <cmath>
...
double round(double x) {
    bool negative = false;
    if (x < 0.0) {
        x = -x;
        negative = true;
    }
    x = std::floor(x+0.5);
    return negative? -x: x;
}

2. In this context a rounding to the nearest integer is not the same thing as a rounding to the nearest int type value. For example, on 32-bit CPU max int is 2147483647 (INT_MAX macros from limit.h). So you can't round 3333333333.3 to int 3333333333 (no such int value) - but you can round it to 3333333333.0. Of course, if you want to round to int, you may use the same method as in round function defined above (no need in floor library call in that case).