0.1 + 0.7% = 0.8

Question

Possible duplicate:
Is JavaScript math broken?

Why in some programming languages ​​does the expression in the header evaluate to true? I tried this in php, ruby ​​and python.

Answer 1

Read What Every Programmer Should Know About Floating-Point Arithmetic.

Answer 2

double TOLERANCE < 1.0E-10;
if(fabs(0.1+0.7-0.8)< TOLERANCE)
{
    std::cout << "0.1 + 0.7 == 0.8" << std::endl;
}
else
{
    std::cout << "0.1 + 0.7 != 0.8" << std::endl;
}

Answer 3

Due to the internal interpretation of floating point numbers, they do not exactly match what you wrote.