A simple calculator | 现代数学启蒙

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Let's break down the code step-by-step:

This line imports the Scanner class from the java.util package, which allows us to read user input.

This line defines a public class named SimpleCalculator. In Java, all executable code must be within a class.

This is the main method, the entry point of any Java application. The main method is where the program begins execution.

String[] args is an array of String arguments passed to the program (not used in this code).

This line creates a Scanner object named scanner, which reads input from the standard input stream (System.in).

This line starts an infinite loop. The loop will continue to execute indefinitely unless explicitly broken.

scanner.nextDouble() reads the next double value entered by the user and assigns it to num1.

Similar to the previous prompt, this line asks the user for a second number and assigns the entered value to num2.

charAt(0) extracts the first character of that String and assigns it to operator.

These lines initialize two variables: result (to store the calculation result) and validOperation (a flag to indicate if the operation is valid).

This switch statement performs different calculations based on the value of operator.

If operator is '+', it adds num1 and num2 and assigns the result to result.
If operator is '-', it subtracts num2 from num1.
If operator is '*', it multiplies num1 and num2.
If operator is '/', it checks if num2 is not zero (to avoid division by zero). If it's not zero, it divides num1 by num2; otherwise, it prints an error message and sets validOperation to false.
If the operator is none of the above, it prints "Invalid operator!" and sets validOperation to false.

This if statement checks if the operation was valid (i.e., no errors occurred). If it was valid, it prints the result.

The closing braces } mark the end of the while loop, the main method, and the SimpleCalculator class.

In summary, this code implements a simple calculator that:

Displays the result or an error message if the operation is invalid (e.g., division by zero or an unrecognized operator).