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My Java code should let the user enter a number and then calculate the factorial of that number and I need to use "for loop" When I enter number 5 it tells me the factorial is 6 when it should be 120. I have tried to watch tutorials with factoring loop but they wont work, i think its because i have "do" command that gets values from calling

Here is the code:

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");

  }

}
Seblor
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Tony Piippola
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    This would be useful: https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems – mkasberg Dec 03 '18 at 20:54
  • Another tip: use editor which can indent your code for you. This way you can notice things like lack of `{` `}` and extra `;` where they are not needed (like right after `if(condition);` or lops `while(conidtion);{...}` `for(...);{...}`). – Pshemo Dec 03 '18 at 21:01
  • Related: [Why do java if statement fail when it ends in semicolon](https://stackoverflow.com/q/12772221) (also applies to loops). – Pshemo Dec 03 '18 at 21:06

2 Answers2

6

If you had used a debugger, then you could tell that it's only executing the multiplication in the calcfactorial method once, and count is already 6 at this point. Reasons:

First, remove the semicolon at the end of the for condition loop. It is acting as the body of the for loop. This makes count equal to newnumber + 1, or 6.

Second, move your print statement after the end of the for loop, but still within the if block. Otherwise you'll get newnumber lines of printouts.

rgettman
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  • Thank you so much! Im still new to java and eclipse so im sorry if i did something stupid... I dont know why my question got downvoted :( But thank you so much man! – Tony Piippola Dec 03 '18 at 21:17
-1

I am not going to fully give away the answer...user azurefrog posted a helpful link on debugging code.

However, your for loop is doing something you don't intend:

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");

    }

}

Reading through this, the line factorial = factorial * count; is just going to do 1*1, 1*2, 1*3, 1*4, 1*5, etc. for whatever is entered to be calculated for factorial. This is not the correct logic.

I recommend thinking through the logic of the for loop a bit more carefully. You should be using the number entered (i.e. 5 for the example you've given) somewhere in that loop.

hmiedema9
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