This is a basic calculator exercise.
This calculator requires two operands and an operator to perform a calculation. You may chain operators without hitting equals.
Like the Google calculator, and unlike the macOS calculator, the equals button does not perform iterative calculations ("2 + = = = = = =" continues to display 2, rather than 2, 4, 6, 8, 10, 12, 14).
If a chain of operators is entered into the calculator, it will only recognize the first operator entered ("2 + - * 2 =" will return 4). To change the operator, you must clear the calculator (AC button) and start again.