<= operator in C++

[GLCODER]

Hi,

I've got a simple question for you guys.

I'm writing a basic program in C++ that looks like this:

float x=0, y=0;
for (; x<=1, y<=1; )
{
cout << sin(x) + cos(y) <<endl;

x +=0.1;
y +=0.1;
}

For some reason though, the calculation is not carried out when x=1 and y=1.
When I set the for loop condition to (x=1.1, y=1.1), the calculation is carried out for x,y=1.0 but not for x,y=1.1

I'm sure there is some simple reason, but I'd like to sort it out now before i make other mistakes.

Thanks in advance,

GLCODER

[Banfa]

The problem is that you can not rely on floats to represent a number exactly (expect for 0) so in the last iteration of your loop you may think you are doing

0.9 + 0.1 = 1

but actually what you are doing is

0.90000001 + 0.100000002 = 1.000000012

which is (as you can see) is > 1.

This is called rounding error and is a known problem when performing floating point calculations. The answer is not to use a float (or double or long double) as the control variable for the loop. Use an integer as the control variable and have the loop iterate for a the required number of iterations (11 in your case)

int ctrl;
float x, y;
 
for( ctrl=0, x=0.0, y=0.0; ctrl<11; x+=0.1f, y+=0.1f, ctrl++)
{
    cout << sin(x) + cos(y) <<endl;
}