我的 Java 关于带阶乘的循环的代码不能正常工作

Question

我的 Java 代码应该让用户输入一个数字，然后计算该数字的阶乘，我需要使用 "for loop" 当我输入数字 5 时，它告诉我阶乘是 6它应该是 120。我曾尝试观看带有因式循环的教程，但它们不起作用，我认为这是因为我有 "do" 从调用

获取值的命令

代码如下：

static Scanner kboard = new Scanner(System.in); //variable to read in values

public static void main(String[] args) {
  int choice = 0;
  String dummy = "";
  String forename = "";
  String surname = "";
  int number = 0;



  do {

    System.out.println("1. display the user name, 2. calculate factorial, 3. exit");
    choice = kboard.nextInt();
    dummy = kboard.nextLine(); //strips out the return 

    if (choice == 1) {
      forename = getforename();
      surname = getsurname();
      displaydetails(forename, surname);
    }

    if (choice == 2) {
      number = getnumber();
      calcfactorial(number);
    }

    if (choice == 3) {
      System.out.println("bye");
    }

  } while (choice != 3);
}


public static String getforename() {

  String newforename = "";

  System.out.println("Please enter your forename ?");
  newforename = kboard.next();
  return (newforename);
} // end getforename

public static String getsurname() {
  /*
  Code to prompt the user to enter a surname
  */
  String newsurname = "";

  System.out.println("Please enter your surname ?");
  newsurname = kboard.next();
  return (newsurname);
} // end getsurname


public static void displaydetails(String displayforename, String displaysurname) {
  /*
  Code will carry out prescribed changes and display the result
  */
  char displayinitial;
  String displayusername = "";

  displaysurname = displaysurname.toUpperCase();
  displayinitial = displayforename.charAt(0);
  displayusername = displayinitial + displaysurname;
  System.out.println("Your username is " + displayusername);

}



public static int getnumber() {


  System.out.println("What numbers factorial do you want to know?");
  int newnumber = kboard.nextInt();
  return newnumber;
}

public static void calcfactorial(int newnumber) {
  int count = 0;
  int factorial = 1;

  if (newnumber > 0) {
    for (count = 1; count <= newnumber; count++); {

      factorial = factorial * count;
      System.out.println("Factorial of " + newnumber + " is: " + factorial);

    }

  } else {
    System.out.println("Number must be positive");

  }

}

Answer 1

如果您使用了调试器，那么您可以看出它只在 calcfactorial 方法中执行一次乘法运算，此时 count 已经是 6。原因：

首先，删除 for 条件循环末尾的分号。它充当 for 循环的主体。这使得 count 等于 newnumber + 1，或 6.

其次，在 for 循环结束后移动打印语句，但仍在 if 块内。否则你会得到 newnumber 行打印输出。

Answer 2

我不会完全给出答案...用户 azurefrog 发布了一篇关于调试代码的有用文章link。

但是，您的 for 循环正在做一些您不希望做的事情：

public static void  calcfactorial(int newnumber)
{
    int count = 0;
    int factorial = 1;

    if (newnumber > 0)
    {
        for (count=1;count<=newnumber;count++);
        {

            factorial = factorial * count; System.out.println("Factorial of "+newnumber+" is: "+factorial);

        }

    }

    else
    {
        System.out.println("Number must be positive");

    }

}

通读一遍，factorial = factorial * count; 行将执行 1*1、1*2、1*3、1*4、1*5 等，无论输入什么都要计算对于阶乘。这不是正确的逻辑。

我建议更仔细地思考 for 循环的逻辑。您应该在该循环的某处使用输入的数字（即您给出的示例中的 5）。

我的 Java 关于带阶乘的循环的代码不能正常工作

My Java code that is about for loop with factorial doesnt work like it should

java

loops

for-loop

factorial