What Every Programmer Should Know About Floating-Point Arithmetic or Why don’t my numbers add up? So you’ve written some absurdly simple code, say for example: 0.1 + 0.2 and got a really unexpected result: 0.30000000000000004 Maybe you asked for help on some forum and got pointed to a long article with lots of formulas that didn’t seem to help with your problem. Well, this site is here to: Explain