How to round up to the next integer?

Question

What is the correct way to round a division of two integers up to the next integer?

int a = 3;
int b = 2;

a / b = ? //should give 2

Is Math.ceil() the right way to go?

@AakashGoyal, that only works for this specific case. What about 4/2, or 6/5? — John, Oct 30 '13 at 17:01
you will get the same value, considering the output will be int. 4/2 -> 5/2 -> 2, 6/5 -> 7/5 -> 1 — Aakash, Oct 30 '13 at 17:02
@AakashGoyal : does not work in most cases. (`b = 1`, or any `b - (a % b) > 1`) — njzk2, Oct 30 '13 at 17:02

Henry · Answer 1 · 2021-09-15T09:03:44.190

35

You can use this expression (assuming a and b are positive)

(a+b-1)/b

edited Sep 15 '21 at 09:03

answered Oct 30 '13 at 16:59

Henry

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This is my favorite answer. It works on any programming language. – Raymond Chenon Nov 06 '20 at 13:31
1

When a = Integer.Max_Value and b = 1234, a + b will cause overflow，so (a -1) / b + 1 is better – 戚锦秀 Jan 07 '23 at 15:48

score 35 · Accepted Answer · answered Oct 30 '13 at 17:00

No, Math.ceil() won't work on its own because the problem occurs earlier. a and b are both integers, so dividing them evaluates to an integer which is the floor of the actual result of the division. For a = 3 and b = 2, the result is 1. The ceiling of one is also one - hence you won't get the desired result.

You must fix your division first. By casting one of the operands to a floating point number, you get a non-integer result as desired. Then you can use Math.ceil to round it up. This code should work:

Math.ceil((double)a / b);

score 4 · Answer 3 · edited Oct 30 '13 at 17:22

The return type of Math.ceil method is double where is, the return type of Math.round is int. so if you want that, the result will be in integer then you should use Math.round method, or else Math.ceil method is fine.

float x = 1654.9874f;     
System.out.println("Math.round(" + x + ")=" + Math.round(x));   
System.out.println("Math.ceil(" + x + ")=" + Math.ceil(x));

Out put

Math.round(1654.9874)=1655

Math.ceil(1654.9874)=1655.0

score 3 · Answer 4 · answered Oct 30 '13 at 17:00

a division between 2 integers (also known as integer division) yields the remaining of the division.

3/2 = 1

To use ceil, you need to make a division that is not integer.:

You can either declare your values as doubles (3.0or 3d) or cast them before dividing:

((double) 3) / ((double) 2) = 1.5

This double value can be used in ceil.

Math.ceil(3.0 / 2.0) = 2.0;

How to round up to the next integer?

4 Answers4

Out put

Linked