How to round up value C# to the nearest integer?

Question

I want to round up double to int.

Eg,

double a=0.4, b=0.5;

I want to change them both to integer.

so that

Answer 1

It is also possible to round negative integers

// performing d = c * 3/4 where d can be pos or neg
d = ((c * a) + ((c>0? (b>>1):-(b>>1)))) / b;
// explanation:
// 1.) multiply:          c * a  
// 2.) if c is negative:  (c>0? subtract half of the dividend 
//                              (b>>1) is bit shift right = (b/2)
//     if c is positive:  else  add half of the dividend 
// 3.) do the division
// on a C51/52 (8bit embedded) or similar like ATmega the below code may execute in approx 12cpu cycles (not tested)

Extended from a tip somewhere else in here. Sorry, missed from where.

/* Example test: integer rounding example including negative*/
#include <stdio.h>
#include <string.h>

int main () {
   //rounding negative int
   // doing something like d = c * 3/4
   int a=3;
   int b=4;
   int c=-5;
   int d;
   int s=c;
   int e=c+10;


   for(int f=s; f<=e; f++) {
      printf("%d\t",f);

      double cd=f, ad=a, bd=b , dd;

      // d = c * 3/4  with double
      dd = cd * ad / bd;

      printf("%.2f\t",dd);
      printf("%.1f\t",dd);        
      printf("%.0f\t",dd);

      // try again with typecast have used that a lot in Borland C++ 35 years ago....... maybe evolution has overtaken it ;) ***
      // doing div before mul on purpose
      dd =(double)c * ((double)a / (double)b);
      printf("%.2f\t",dd);

      c=f;
      // d = c * 3/4  with integer rounding
      d = ((c * a) + ((c>0? (b>>1):-(b>>1)))) / b;
      printf("%d\t",d);
      puts("");
  }
 return 0;
}

/* test output
in  2f     1f   0f cast int   
-5  -3.75   -3.8    -4  -3.75   -4  
-4  -3.00   -3.0    -3  -3.75   -3  
-3  -2.25   -2.2    -2  -3.00   -2  
-2  -1.50   -1.5    -2  -2.25   -2  
-1  -0.75   -0.8    -1  -1.50   -1  
 0   0.00    0.0     0  -0.75    0  
 1   0.75    0.8     1   0.00    1  
 2   1.50    1.5     2   0.75    2  
 3   2.25    2.2     2   1.50    2  
 4   3.00    3.0     3   2.25  3    
 5   3.75    3.8     4   3.00   

// by the way evolution: 
// Is there any decent small integer library out there for that by now?

Answer 2

The .NET framework uses banker's rounding in Math.Round by default. You should use this overload:

Math.Round(0.5d, MidpointRounding.AwayFromZero)  //1
Math.Round(0.4d, MidpointRounding.AwayFromZero)  //0

Answer 3

Use Math.Ceiling to round up

Math.Ceiling(0.5); // 1

Use Math.Round to just round

Math.Round(0.5, MidpointRounding.AwayFromZero); // 1

And Math.Floor to round down

Math.Floor(0.5); // 0