c++ why does ((1 / 2) * 2) return 0

Question

first time I'v posted here but I must know what's wrong with this simple peace of code:

#include <iostream>

using namespace std;

int main()
{
    double test = (1 / 2) * 2;
    cout << test << endl;
    return 0;
}

when ever I run this the code it displays 0, should I be casting something, it happens regardless of what compiler I use and it returns even stranger results if the '1' is divided be some form of decimal.

Because 1 and 2 are `int`s. And by default, all numbers are `int`s. — Maroun, May 12 '15 at 10:23

score 8 · Accepted Answer · answered May 12 '15 at 10:23

8

Because in integer maths 1 / 2 == 0 and 0 * 2 == 0.

Try with 1.0 and 2.0 instead.

answered May 12 '15 at 10:23

trojanfoe

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score 2 · Answer 2 · answered May 12 '15 at 10:25

2

In (1 / 2) both the 1 and 2 are integers which means that the result is also an integer. This means the expression returns 0. 0 * 2 is 0.

To get the result you want, try (1.0 / 2.0)

answered May 12 '15 at 10:25

doron

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1

It's enough to `.0` only one side. – Maroun May 12 '15 at 10:26

Ashot Khachatryan · Answer 3 · 2015-05-12T10:27:39.087

1

If you want to get right result you need to write:

#include <iostream>

using namespace std;

int main()
{
  double test = ((double)1 / 2) * 2;
  cout << test << endl;
  return 0;
}

edited May 12 '15 at 10:27

answered May 12 '15 at 10:25

Ashot Khachatryan

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Explanation needed. Also it's enough to cast only one side, the other will be implicitly cast. – Maroun May 12 '15 at 10:25
1

Also, don't use C-style casts. – Baum mit Augen May 12 '15 at 10:27

score 0 · Answer 4 · answered May 12 '15 at 10:26

0

You're using int instead of double.

Fixing...

#include <iostream>

using namespace std;

int main()
{
    double test = (1.0 / 2.0) * 2.0;
    cout << test << endl;
    return 0;
}

answered May 12 '15 at 10:26

Tarod

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c++ why does ((1 / 2) * 2) return 0

4 Answers4