Nearest integer function

[Marcial]

I know it's a basic question, but, can you please tell me how can I take the nearest integer of a floating variable? For example, if C=1.25, I want to take Cint=1; if C=1.5, Cint=2, and so on. Also, I want to secure that it works with negative numbers as well.

[Dy7SLyTq]

double mydub = 3.14;
int myint = mydub;
cout<< mydub <<" "<< myint;

[Marcial]

Thanks, DTScode, but I'm having these problems:

It gives this warning:
[Warning] converting to 'int' from 'double'

It still compiles, but the double number is only rounded down, never up. 3.2 and 3.999 return 3.

Further, when I try to enter the floating value myself with cin, it returns 0.

[Smac89]

http://stackoverflow.com/a/485546/2089675

A simple extension to make it work for negative numbers:

double round(double d)
{
  	return d < 0 ? ceil(d - 0.5) : floor(d + 0.5);
}

Or if you want to return just int not double:
http://stackoverflow.com/a/4660122/2089675

Available in c++11 cmath library:
http://stackoverflow.com/a/11101890/2089675
Round function => http://en.cppreference.com/w/cpp/numeric/math/round

[alsade]

you can just add an If statment like this (relying on previous response) :

if (mydub>myint+0.5)
   myint=myint+1;

dont forget u can do this only after the casting.

[Marcial]

This isn't working, it returns errors. This "return floor" seems to be making some mess, the prompt only blinks at the screen. I'm trying this:

int main () {
    double d=5.6;
    double round(double d);
{
	double neg = d < 0 ? -1 : 1;
  	return floor(d + (neg * 0.5));
}
 
                 system ("PAUSE");
                 return 0;

}

[Smac89]

Why did you declare the function inside main? Also the code I posted is updated and one more link included which contains a link to the official round function for c++

[Marcial]

Smac89, where shall I declare the function? If before main, it returns

expected unqualified-id before '{' token
expected `,' or `;' before '{' token

How can I know if my version of C++ is more recent than 11?

[Smac89]

The most recent version of c++ (to my knowledge) is c++14, but you just need c++11 for this.

If you are using an IDE, you will have to check the website for the specific IDE to see if the current version supports c++11.

If you use a terminal, try compiling the program with the flag -std=c++11 or -std=gnu++11

Declare the function before main:

#include <cmath>
#include <iostream>

double round(double d)
{
    return d < 0 ? ceil(d - 0.5) : floor(d + 0.5);
}

int main()
{
    double d = 3.75;
    cout << round(d) << endl;
    return 0;
}

[Marcial]

Thanks a lot, Smac89. It's working perfectly now!

[JLBorges]

#include <iostream>
#include <cmath> // for std::lround()
#include <iomanip>

int main()
{
    const float a[] = { -1.5f, -1.25f, -0.6f, -0.1f, 0.0f, 0.49f, 0.50f, 1.25f, 1.5f } ;

    std::cout << std::fixed << std::setprecision(2) << std::showpos  ;

    for( float f : a )
    {
        // http://en.cppreference.com/w/cpp/numeric/math/round
        const long v = std::lround(f) ;

        std::cout << f << " => " << v << '\n' ;
    }
}

http://coliru.stacked-crooked.com/a/dfbb745b61a634b8