Fractions

[JohanCarlsen]

Hello, I'm trying to write the following:

double dt = 1/5; std::cout << dt << endl;

But here, instead of dt being 0.2, it is 0.. Why is that?

[JohanCarlsen]

Never mind, I solved it. I had to do: double num1=1, num2=5; double dt = num1/num2;

[anderkve]

Hi @JohanCarlsen,

You've encountered what's called integer division. You can read about the mathematics here: https://mathworld.wolfram.com/IntegerDivision.html Short story is that with integer division, any fractional part (remainder) is discarded.

C++ will interpret both 1 and 5 as integers, and thus perform integer division. With integer division 1/5 = 0, so what's happening is that you have effectively written

double dt = 0;

However, if you include a decimal point for either 1 or 5 (or both), i.e. write 1. or 5. (or both), C++ will perform regular division of floating-point numbers. So this code will give you what you expect:

double dt = 1./5;
std::cout << dt << endl;