Question

While doing my homework I noticed something really strange that I just can’t figure out why.

int x = 5;
cout << pow(x, 2);

The result is 25. That’s fine. But if I write the same program like this:

int x = 5;
int y = pow(x, 2);
cout << y;

The result is 24!

When x is 2, 3, 4, 6, 7, 8 no problem, but with 5, 10, 11, 13 etc. result is 1 lower than it should be.

Same thing with if().

for (int x = 1; x <= 20 ; x++) {
    if (x * x == pow(x, 2)) 
    cout << x << endl;
}

It prints out numbers 1, 2, 3, 4, 6, 8, 12, 16.

Answer 1

std::pow() returns a floating point number. If the result is for instance 24.99999999 and you cast it to int, it will be cut off to 24.

And that is what you do in the 2nd code example.
cout does not convert to int and outputs the correct result in the 1st code example.