Convert double to int

[thetinman]

I need to know how to convert a number of the type double to a number of the type int. My double numbers have a lot of digits behind the decimal point and I need to have these properly rounded(not a 'ceil' or 'floor' type of rounding) after the conversion has taken place. Is there a simple way to do this? What is the best way to do it? Below is some code that does not work.

#include <stdio.h>
#include <math.h>

int main()
{
    double x, y;
    int a, b;
    x = 3.322884; 
    y = 3.700219;
    a = x;
    b = y; 
    printf("a = %d, b = %d\n", a, b);
}

[quzah]

Add whatever your rounding point is to it, then just assign it to an integer.


Quzah.

[Br5an]

Something like this?

#include <stdio.h>
#include <math.h>

int main()
{
    double x, y;
    int a, b;
    x = 3.322884; 
    y = 3.700219;
    x += .5;
    y += .5;
    a = x;
    b = y; 
    printf("a = %d, b = %d\n", a, b);
}

[Lionmane]

Ditto...

mw

[quzah]

That's why we both said to add the rounding point and then assign to an int.


Quzah.

[thetinman]

Add .5 and round down. Thanks, it worked.

[Dave_Sinkula]

Add 0.5 and truncate, I might say. But do you also need to consider negative values?

#include <stdio.h>

int foo(double value)
{
   return value < 0 ? value - 0.5 : value + 0.5;
}

int bar(double value)
{
   return value + 0.5;
}

int main()
{
    double x = 3.322884;
    double y = 3.700219;
    printf("foo(%f) = %d, foo(%f) = %d\n", x, foo(x), y, foo(y));
    printf("bar(%f) = %d, bar(%f) = %d\n", x, bar(x), y, bar(y));
    x = -x;
    y = -y;
    printf("foo(%f) = %d, foo(%f) = %d\n", x, foo(x), y, foo(y));
    printf("bar(%f) = %d, bar(%f) = %d\n", x, bar(x), y, bar(y));
    return 0;
}	

/* my output
foo(3.322884) = 3, foo(3.700219) = 4
bar(3.322884) = 3, bar(3.700219) = 4
foo(-3.322884) = -3, foo(-3.700219) = -4
bar(-3.322884) = -2, bar(-3.700219) = -3
*/

Then perhaps it might be: increase distance from zero by 0.5.

[n7yap]

thetinman,

If your compiler supports C99, you can use lround(), it takes a double and returns a long.