Question

public static void main (String args [])  {
    Scanner sc = new Scanner(System.in);
    int number;
    int factor=1;
    System.out.println("Enter a number to find the factorial of it: ");
    number= sc.nextInt();
    factor=factorial(number);
    if (number < 1 || number > 10)
    {
        System.out.println("Invalid!! the number has to be between 1 and 10");
    }
    System.out.println("The factorial of  "+number+" is = " +factor);        
}

public static int factorial (int number) {
    int result = 1;
    if (number < 1 || number > 10)
    {
        System.out.println("Invalid!! the number has to be between 1 and 10");
    }
    else {
        for(int x=1; x<=number; x++ ) {
            result= result*x;
        }
    }
    return result;
}

我的代码工作正常但是如果我输入11，它会显示无效消息，它还会计算11我不想要的阶乘。

Answer 1

您应该移动检查用户输入范围的代码，使其高于对factorial()函数的调用：

public static void main (String args [])  {
    Scanner sc = new Scanner(System.in);
    int number;
    int factor=1;
    System.out.println("Enter a number to find the factorial of it: ");
    number= sc.nextInt();
    if (number < 1 || number > 10) {
        System.out.println("Invalid!! the number has to be between 1 and 10");
    } else {
        factor=factorial(number);
        System.out.println("The factorial of  "+number+" is = " +factor);
    }
}

请注意，对factorial()和println()语句的调用现在都在新的else块内。因此，如果用户输入的数字无效，则程序给出的唯一响应是错误消息。

如果您还希望在factorial()中进行错误检查，最明确的方法可能是在给出无效输入时抛出IllegalArgumentException：

public static int factorial (int number) {
    int result = 1;
    if (number < 1 || number > 10)
    {
        System.out.println("Invalid!! the number has to be between 1 and 10");
        throw new IllegalArgumentException("Factorial input has to be between 1 and 10");
    }

    // rest of your code....
}

应用函数方法（调用函数）进行阶乘

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