Computes the absolute value of a number.
x: the number
x: if x is greater than or equal to 0. -x: if x is less than 0.
Because of the way the abs() function is implemented, avoid using other functions inside the brackets, it may lead to incorrect results.
abs(a++); // avoid this - yields incorrect results
a++; // use this instead - abs(a); // keep other math outside the function