Do you remember the basic rule of arithmetic that "changing the order of the numbers we are adding doesn't change the sum"? It's called the **commutative law**.

A binary operation is commutative since swapping operands gets you the same result. Obviously, addition is a commutative operation: _3 + 2 = 2 + 3_.

But is subtraction a commutative operation? Of course not: _2 - 3 ≠ 3 - 2_. In programming, this law applies just like it does in arithmetic.

Moreover, most of the operations we face in real life are not commutative. Here is the conclusion: always pay attention to the order of things you work with.
