The concept of negation is to take a value and change its sign, that is: fip it. If it positive make it negative and if it is negative make it positive. Mathematically, it is the following C++ code example, given that money is an integer variable with a value of 6:
-money money * -l
The above two expressions evaluate to the same value. In the first line, the value in the variable money is fetched and then it's negated to a negative 6. In the second line, the value in the variable money is fetched and then it's multiplied by negative 1 making the answer a negative 6.