Program not entering if statement

Question

In my python program, an if statement is not being entered. I have simplified the code to the following:

x = -5
while x < 5:
    if (x == 0):
        print 0
    x += .01

This program does not output anything.

However, changing the last line to x += .5 makes the program output 0. What's the problem?

Answer 1

Floating point number representation might not be accurate enough. You should never test for zero equality but instead use something along

if (abs(x) < 1E-10) ...