C++ Rounding and Truncation

Opeth · 09-17-2005, 06:19 PM

Could anybody tell me which way would round up a float when turning it into an integer? I have a problem where I must use cin to take in 5 decimal numbers and then display them as the nearest integers. I'm not sure if just assigning the decimals into ints would truncate or round them. But if it truncates them what would be a way to round them up? Also, I'm restricted to the simplest things in c++ right now, not even loops or anyting, as we are only on chapter 2 in the class.

glvgfz · 09-17-2005, 06:41 PM

In C, you have

Quote:

double round(double x);
float roundf(float x);
long double roundl(long double x);

defined in <math.h>

In C++, you would probably want to use equivalent functions in <cmath>.

btw, nice taste in music.

glvgfz · 09-17-2005, 06:44 PM

If you want to round up or down, use ceil() and floor() functions.

look at round(3)

Code:

man 3 round

and look at where it says "SEE ALSO"

deiussum · 09-17-2005, 06:51 PM

Or if you don't want to use any function at all, the following is a quick and dirty way to do it. (The casts are there just to get rid of the warnings.)

Code:

#include <iostream>
using namespace std;

int main()
{
    float f1 = 0.5;
    float f2 = 0.6;
    float f3=0.3;
    int i1 = static_cast<int>(f1 + 0.5);
    int i2 = static_cast<int>(f2 + 0.5);
    int i3 = static_cast<int>(f3 + 0.5);

    cout << i1 << endl
        << i2 << endl
        << i3 << endl;

    return 0;
}

Opeth · 09-17-2005, 07:16 PM

Thanks to all for your suggestions, but I probably should have been more clear in that last part of my post in that this was meant to be done without any functions. He says that the only functions we are learning this semester are cout and cin, which sucks, so I guess I'll take some time when I get a little more familiar to mess around with others. Thank you a lot for that deiussum, although I was hoping for less typing. I guess it's just that c++ chooses to truncate rather than round.

glvgfz, Opeth rock indeed.