How do I make it so I don't have to preset the number of grades that can be entered?

[David Vach]

I had to create a project for my computer science class, and I realized that my teacher wants the user to be able to input as many grades as they want. I created a class that has you set the number of grades that you are going to enter before hand, however I am not sure how I can give them the ability to put in as many grades as they want at once. I was thinking that you could create a while loop and have a key work trigger the end of the sequence, but I'm not sure how to do that. I want to keep the prompt before the user enters their grade of "Enter grade number (#)" before the user enters their grade. Then it should go on and one until a keyword prompts it. I am rather new to coding, only just started the class this year. Here is my code:

import java.io.*;
import java.util.*;

public class gradeCalculator
{
    public static void main(String [] args)
    {
        Scanner input = new Scanner(System.in);
        
        double average;
        String YoN;
        int numberGrades, i;
        
        double sum = 0.0;
        double grade = 0.0;  
        System.out.println("Welcome to Grade Calculator!");
        
        System.out.println("\nWould you like to enter your grades?");
        YoN = input.next();
        
        if(YoN.equalsIgnoreCase("yes"))
        {
            System.out.println("How many grades are you going to enter?");
        }
        else if( YoN.equalsIgnoreCase("no"))
        {
            System.out.println("Come back when you have grades to enter");
            System.exit(0);
        }
        while (!YoN.equalsIgnoreCase("yes"))
        {
            System.out.println("That was not a vaild input, please try again");
            System.out.println("\nWould you like to enter your grades?");
            YoN = input.next();
            if(YoN.equalsIgnoreCase("yes"))
            {
                System.out.println("How many grades are you going to enter?");
            }
            else if( YoN.equalsIgnoreCase("no"))
            {
                System.out.println("Come back when you have grades to enter");
                System.exit(0);
            }
        }
 
        numberGrades = input.nextInt();
        
        for(i=0; numberGrades > i ;i++)
        {
            System.out.print("Enter grade number " + (i+1) + " : ");
            grade = input.nextDouble();
            sum+= grade; 
        }
        
        average =  sum/numberGrades;       
        System.out.println("Your average is = " + average + "%");
        
        if (100 == average)
        System.out.println("\nAmazing, you got an A+!");
        if (100 > average && average >= 89.5)
        System.out.println("\nCongrats, you got an A");
        if (89.5 > average && average >= 79.5)
        System.out.println("\nGood job, you got a B");
        if (79.5 > average && average >= 69.5)
        System.out.println("\nWell, you still got a C");
        if (69.5 > average && average >= 59.5)
        System.out.println("\nYou got a D, but hey you still passed");
        if (59.5 > average)
        System.out.println("\nI'm sorry, but you failed. You got an F. Try again next year");
        
        System.out.println("If you would like to calculate you grades again, please relaunch the program.")
    }
}

[David Vach]

Also how could I create a message if someone input more than 100%, for it to ask them if they are sure this is the correct value and if they respond yes, it keeps the value, and if no, it makes them re enter it?

[Knute Snortum]

        numberGrades = input.nextInt();
         
        for(i=0; numberGrades > i ;i++)
        {
            System.out.print("Enter grade number " + (i+1) + " : ");
            grade = input.nextDouble();
            sum+= grade; 
        }

Both questions can be answered using a while loop (or a do/while loop).  It looks like you know how to code a while loop, so let's start with that.  How would a user entering grades, tell the program they want to stop?  Press the <enter> key?  Enter -1?  Give it some thought and try stuff out.

[Campbell Ritchie]

I would suggest you shou‍ld move most of that code out of the main method. I think you shou‍ld have a result class, which incorporates the grades, calculates the results, etc.
I would also suggest you use else if rather than straight if statements.
Also consider the use of operators. The >= and <= operators are harder to understand that < and >. Also, 100 > average is much more difficult to understand than average < 100. You can make if statements really easy to understand or really difficult to understand by the operators you use.
Why 79.5 (etc)? What will you get for a mark of 79.6?

[David Vach]

Ive been trying different while loops for the past 2 hours, as that was what I thought might work as well, but I still am not getting it. How should my while loop for this instance start? Maybe that's where my error is.

[David Vach]

Here is what I have so far. It only kind of works, allowing me to enter 1 number then I have to type end to end it.
Here is the code:

import java.io.*;
import java.util.*;
 
public class gradeCalculator
{
    public static void main(String [] args)
    {
        Scanner input = new Scanner(System.in);
         
        double average, g;
        String YoN;
        int numberGrades, counter;
         
        double sum = 0.0;
        double grade = 0.0;  
        System.out.println("Welcome to Grade Calculator!");
         
        System.out.println("\nWould you like to enter your grades? yes/no");
        YoN = input.next();
         
        if(YoN.equalsIgnoreCase("yes"))
        {
            System.out.println("How many grades are you going to enter?");
        }
        else if( YoN.equalsIgnoreCase("no"))
        {
            System.out.println("Come back when you have grades to enter");
            System.exit(0);
        }
        while (!YoN.equalsIgnoreCase("yes"))
        {
            System.out.println("That was not a vaild input, please try again");
            System.out.println("\nWould you like to enter your grades?");
            YoN = input.next();
            if(YoN.equalsIgnoreCase("yes"))
            {
                System.out.println("How many grades are you going to enter?");
            }
            else if( YoN.equalsIgnoreCase("no"))
            {
                System.out.println("Come back when you have grades to enter");
                System.exit(0);
            }
        }
  
        YoN = input.next();

        while (YoN.equalsIgnoreCase("start"))
        {
            grade = 0;
            counter = 1;
            System.out.println("Enter grade number " + counter + ":");
            grade = input.nextDouble();
            counter++;
            sum+= grade;
            YoN = input.next();
            
            if(YoN.equalsIgnoreCase("end"))
            {
               average =  sum/counter;       
               System.out.println("Your average is = " + average + "%");
       
               if (100 == average)
               System.out.println("\nAmazing, you got an A+!");
               if (100 > average && average >= 89.5)
               System.out.println("\nCongrats, you got an A.");
               if (89.5 > average && average >= 79.5)
               System.out.println("\nGood job, you got a B.");
               if (79.5 > average && average >= 69.5)
               System.out.println("\nWell, you still got a C.");
               if (69.5 > average && average >= 59.5)
               System.out.println("\nYou got a D, but hey you still passed.");
               if (59.5 > average)
               System.out.println("\nI'm sorry, but you failed. You got an F. Try again next year!");
               else
               System.out.println("If you would like to calculate you grades again, please relaunch the program.");
            }
        }
    }
}

[Knute Snortum]

The thread seems to have gone here.  Locking this thread.