A simple 8-digit electronic calculator contains the following buttons: “1234567890+-*/=” (no quotes). It can be divided into the following categories:
Digit: “1234567890”
You can input any number with digital buttons (ignore leading zero). Notice, the LED of calculator can only display 8 digits. So when the number of digits large than eight, only the first eight digits will be retained. And when the number of one result’s digits large than eight, error occurs.
Operator: “+-*/”
For simplicity, all operations are integer operations. Some continuous operators, the last one is valid. When an operator button is pressed, the calculation before that will be completed.