spoocter:
ok thank you can you explain me what does stdlib contain and why do i need it and why do i use abs
http://www.cplusplus.com/reference/clibrary/cstdlib/
The #include isn't necessary because the it's included anyway, but it contains abs() which gives you the absolute value of a number. When you need to get the distance between two numbers, you take the absolute value of their difference. That's really just a basic algebra concept.