Question

So I am trying to write a simple program for my Java class and I have asked the teacher for help however, this is a distance learning class and am not getting much help from that direction. So here I am.

The problem we have been asked to solve is to create a program that will
(1) ask the user for a number ,
(2) find the sum of all user defined numbers ,
(3) find the average of these numbers ,
(4) then out put them back to the user.

I use the numbers not only to line through things I have finished but because they must be separate modules to be called.

How can i get the userNum variable to update durring the while statments. Currently they are not. OR is there a simpler way to do this that im overlooking. Any help is greatly appreciated. Thank you.

public class P2 {

   public static void main(String[] args) {

        int userNumCount = 1;

        double userNum = input();
        double userSum = sum(userNum);
        double userAverage = average(userSum, userNumCount);

        sum(userNum);

        while (userNum != 0 && sum(userNum) <= 100){
            ++userNumCount;          
            output(userSum, userAverage);
            input();
            sum(userNum);
            average(userSum, userNumCount);
        }//end else
        while (userNum != 0 && sum(userNum) >=100){
            ++userNumCount;
            JOptionPane.showMessageDialog (null, "Warning, your sum is currently over 100!!!!!"); 
            output(sum(userNum), userAverage);
            input();
            sum(userNum);
            average(userSum, userNumCount);
    }//end else
        if (input() == 0){
            output(userSum, userAverage);
            JOptionPane.showMessageDialog (null, "Thank you for using this program have a nice day.");
    }//end else if


    }//end main module
    public static double input(){
        String userNumString;
        userNumString = JOptionPane.showInputDialog("Please enter your number or input 0 to end the program.");
        double userInput = Double.parseDouble (userNumString); 
        return userInput;
    }//end input module
    public static double sum(double userNum){  
        double userSum =+userNum;
        return userSum;
    }//end sum module
    public static double average (double userSum, int userNumCount){
        double userAverage = userSum/userNumCount;
        return userAverage;
    }//end average module
    public static void output (double userSum, double userAverage){
        JOptionPane.showMessageDialog (null, "The sum of the numbers input so far is: " + userSum + ". And the Average is " + userAverage + "." );
    }//end output module
}//end class

Answer 1

This is incorrect.

public static double sum(double userNum){  
    double userSum =+userNum;
    return userSum;
}

In a basic pseudo-language this is happening each time this method is called

receive userNum
create userSum
set userSum = 0
add userNum to userSum
give userSum

each time the method will return the value it is given, not the running total I think you are expecting.

If you have two variables declared with the same name, they are still different. What you want to do is refer to the same variable, to do this you need to have the references in the scope where the variable is declared.

to get the running total

public class P2 {

    public static double userSum = 0; 
    //because this is a public member it's scope is global i.e. you can refer to it anywhere.

    ...
    public static void main(String[] args) {
    ... 
    /* do not declare userSum here.
       if you do any reference to userSum will use the local variable 
       not the global variable.
       double userSum = 0; <-- declare local variable it's scope is until the 
                               end of this method nothing outside the method 
                               can see it but you can pass it as a parameter
       userSum = 1; <-- local variable is set to 1
       P2.userSum = 2; <-- local variable is set to 1 global is set to 2
    */
       input();// for this the input method is called and returns a value,
               // but you haven't said to put it anywhere so java will throw it away
               // all that effort for nothing.

       userNum = input(); // in this case it will put the new value in userNum.
    }

    public static double sum(double userNum){  
        userSum =+userNum; // do not declare userSum use it from the class context
        return userSum;
    }

    ...

}

for further reference scope