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c++rounding
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Reputation: 341

Simplest Way of Rounding Up the Average in C++

int a, b, c = 0;
c = (a+b)/2;

In this code, if both "a" and "b" are even (Example 1), then there's no problem. But if one of them is odd (Example 2), then the answer will have +0.5. I want to round it up.

Example 1.

a=4, b=10

c will be = 7 This is OK.

Example 2.

a=3, b=4

c will be = 3.5 And I want c to be rounded up and become 4 instead.

Upvotes: 0

Views: 4315

Answers (6)

Vinz
Vinz

Reputation: 3198

The easiest thing would be to use + 1 after the result if the result is not round (what the ceil function would do by default for you)

int a, b, c = 0;
if ((a + b) % 2 == 1)
   c = ((a+b)/2) + 1;
else
   c = (a+b)/2;

Demo: https://ideone.com/AmgDUt

Upvotes: 0

vsoftco
vsoftco

Reputation: 56557

First of all, make c a double, then use

c = (a + b)/2.0

otherwise you have truncation due to division of ints being casted to int. In this way, (a + b) / 2.0 is a double, due to the denominator being a double, so you don't have any truncation.

Next, use the function std::round from C++11, or std::floor/std::ceil, depending on what exactly you want

Alternatively, you can keep c and int but do

c = std::round( (a + b) / 2.0 ); // rounding to nearest integer, C++11

or 

c = std::floor( (a + b) / 2.0 ); // rounding down

or 

c = std::ceil( (a + b) / 2.0 ); // rounding up

If you don't want any warnings, can also explicitly cast the result of std::floor/std::ceil/std::round back to int, like

c = static_cast<int>(std::round( (a + b) / 2.0 )); // now we tell the compiler we know what we're doing

Upvotes: 0

shauryachats
shauryachats

Reputation: 10385

The simplest thing is to use the ceil() function from <math.h>.

int a, b, c = 0;
c = (int) ceil((float)(a+b)/2);

Upvotes: 0

swang
swang

Reputation: 5249

int a, b, c = 0;
c = (a+b+1)/2;

Upvotes: 0

Sebastian Redl
Sebastian Redl

Reputation: 71989

First off, you're wrong. c is an integer, so it can't be 3.5. Furthermore, a, b and 2 are all integers, so the division is integer division, so it can't result in 3.5 either. It will be rounded towards zero, so it will be 3.

That said, to get integer division by 2 to round up instead of down, simply add 1 before dividing. (14 + 1) / 2 == 7, so that's still right. (7 + 1) / 2 == 4, so that's correct too.

Upvotes: 8

Lawrence Aiello
Lawrence Aiello

Reputation: 4638

Use the ceil function. It will always round up whatever number you put in it.

Upvotes: 1

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