9.24

今天的课都是硬课啊!!!!
import java.util.Random;

public class RandomArithmetic {
public static void main(String[] args) {
Random random = new Random();
int numOperations = 30;

    for (int i = 0; i < numOperations; i++) {  
        int num1 = random.nextInt(90) + 10; 
        int num2 = random.nextInt(90) + 10;  
        String operator = getRandomOperator();  
        double result = evaluate(num1, num2, operator);  
        System.out.printf("%d %s %d = %.2f%n", num1, operator, num2, result);  
    }  
}  

private static String getRandomOperator() {  
    Random random = new Random();  
    int operation = random.nextInt(4); 

    switch (operation) {  
        case 0: return "+";  
        case 1: return "-"; 
        case 2: return "*"; 
        case 3: return "/";   
        default: return "+"; 
    }  
}  

private static double evaluate(int num1, int num2, String operator) {  
    switch (operator) {  
        case "+":  
            return num1 + num2;  
        case "-":  
            return num1 - num2;  
        case "*":  
            return num1 * num2;  
        case "/":  
            if (num2 != 0) {  
                return (double) num1 / num2; 
            } else {  
                return 0; 
            }  
        default:  
            return 0;  
    }  
}  

}