Operator Precedence
When a calculation contains more than one operator, C++ follows order of operations rules to decide which part to calculate first.
For example, multiplication happens before addition:
Example
int result1 = 2 + 3 * 4; // 2 + 12 = 14
int result2 = (2 + 3) * 4; // 5 * 4 = 20
cout << result1 << "\n";
cout << result2 << "\n";Why Does This Happen?
In 2 + 3 * 4 , the multiplication is done first, so the answer is 14 .
If you want the addition to happen first, you must use parentheses: (2 + 3) * 4 , which gives 20 .
Tip
Always use parentheses ( ) if you want to make sure the calculation is done in the order you expect. It also makes your code easier to read.
Order of Operations
Here are some common operators in C++, from highest to lowest priority:
- () - Parentheses
- * , / , % - Multiplication, Division, Modulus
- + , - - Addition, Subtraction
- > , < , >= , <= - Comparison
- == , != - Equality
- && - Logical AND
| - | - Logical OR |
|---|
- = - Assignment
Another Example
Subtraction and addition are done from left to right, unless you add parentheses:
Example
int result1 = 10 - 2 + 5; // (10 - 2) + 5 = 13
int result2 = 10 - (2 + 5); // 10 - 7 = 3
cout << result1 << "\n";
cout << result2 << "\n";Remember
Parentheses always come first. Use them to control the order of your calculations.