How do I round this int up

Question

Is there any way to round systemGuess up. In this case the outcome of systemGuess is 5.5 I want it to be 6 how do I do this?

See code below:

 int main(void){

    int systemGuess = 0;
    stystemGuess = (10 - 1)/2 + 1;
    printf(" %d ", stystemmGuess);
}

If you want to round normally, add `.5` to the total before assigning to stystemGuess. — Riley, Oct 04 '16 at 14:27
It depends on the rounding rules you are trying to apply. Do you want to round all results of integer division up, or round to the nearest integer with a tie-break rule for .5, or what? — Ian Abbott, Oct 04 '16 at 14:53

score 2 · Accepted Answer · answered Oct 04 '16 at 14:27

2

Use floating point division and ceil:

stystemGuess = ceil((10 - 1)/2.0) + 1;

If you want to round 0.4 down, use round instead.

answered Oct 04 '16 at 14:27

orlp

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"If you want to round 0.4 down, " --> use `floor()`. `round()` is for rounding to nearest and ties handled in a defined way. – chux - Reinstate Monica Oct 04 '16 at 15:27
@chux I meant 'if you want to round `0.5` up and `0.4` down'. – orlp Oct 04 '16 at 15:28
OK - OP's is a bit unclear about quotients in the (0.0 ... 0.5) range. – chux - Reinstate Monica Oct 04 '16 at 15:31

chux - Reinstate Monica · Answer 2 · 2016-10-04T16:27:16.957

OP wants to perform an integer division with the result rounded-up.

// If the quotient fraction > 0, return next larger number.
unsigned udiv_ceiling(unsigned n, unsigned d) {
  return (n + d - 1)/d;
}

// If the quotient fraction >= 0.5, return next larger number.
unsigned udiv_nearest_ties_up(unsigned n, unsigned d) {
  return (n + d/2)/d;
}

stystemGuess = udiv_ceiling(10 - 1, 2) + 1;
// or
stystemGuess = udiv_nearest_ties_up(10 - 1, 2) + 1;

Additional code needed to handle negative numbers and in corner cases, protect against n + d - 1 overflow.

jfschaefer · Answer 3 · 2016-10-04T14:30:13.890

0

You can use

systemGuess = (10 - 1)/2.0 + 1 + 0.5;

The problem is that you do integer calculation. So e.g. 9/2 is 4. If you use 9/2.0 you have floating point division, which gives you 4.5. Adding 0.5 in the end gives you 6.0 instead of 5.5, so when storing it in systemGuess, you get 6 instead of 5.

edited Oct 04 '16 at 14:30

answered Oct 04 '16 at 14:27

jfschaefer

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Not everyone here is dutch. – orlp Oct 04 '16 at 14:27
Sorry, I saw the question with those Dutch (?) variables names. Changed it – jfschaefer Oct 04 '16 at 14:37

score 0 · Answer 4 · edited May 23 '17 at 11:48

Integer division in C truncates toward 0, so if you do the math on the other side of 0 (i.e., on negative numbers), it will "round up". You might do this by subtracting an amount from the dividend and adding half that amount back to the result:

int main(void)
{
    int systemGuess = 0;
    //systemGuess = (10 - 1)/2 + 1;
    systemGuess = (10 - 1 - 20)/2 + 1 + 10;
    printf(" %d ", systemGuess);
}

Probably in your real program there is a more elegant way to make this happen.

score 0 · Answer 5 · answered Oct 04 '16 at 14:37

Here you go:

#include <stdio.h>
#include <stdlib.h>

int divide(int x, int y);

int main(void){

    int systemGuess = 0;

    int x = 10-1;
    int y = 2; 

    systemGuess = divide(x,y) + 1;

    printf(" %d ", systemGuess);

}

int divide(int x, int y) {
   int a = (x -1)/y +1;
   return a;
}

How do I round this int up

5 Answers5