用给定范围内用户的双精度数填充数组

Question

So it's time to come back to the users of stackoverflow for help again on an assignment.

I'm supposed to fill an array with a size of 10 with doubles given from the user. The entered numbers are supposed to be grades so they have to be in the range of 0 - 100. Anything out of the range (more, less, or incorrect characters) are not saved to the array and the user is prompted to try again at the given index of the array. After either the array is filled to the max value or the user presses enter to skip, the program is supposed to return the grades entered in order and display the average.

public static final SIZE = 10;

Scanner userIn = new Scanner(System.in);
double[] grades = new double [SIZE];
int counter = 0;
int counterList = 1;
boolean exit = false;
String sTemp = "";
double gradeNum = 0;
double avrGrade = 0.0;
double sum = 0;

while((counter < SIZE) && (!exit)) {
    System.out.println("Enter grade " + counterList +
            ", or press enter to quit.");
    sTemp = userIn.nextLine();
    counterList++;
    if(sTemp.length() < 1) {
        exit = true; //ending for loop
    } else {
        gradeNum = Double.parseDouble(sTemp);
        grades[counter] = gradeNum;
        counter++;
    } //else statement
} //end of while loop
counterList = 1;
System.out.println("You entered " + counter + " grades total.");
for(int i = 0; i <= counter; i++) {
    System.out.println("Your grade " + counterList + " is " + grades[i]);
    counterList++;
}
for(int i = 0; i < grades.length; i++)
    sum += grades[i];
System.out.println("The average grade is: " + sum / grades.length);

So I finished taking my user's input and calculating the average but I'm having trouble setting the range and not saving the invalid inputs. I also feel like once I started to struggle I got really sloppy and there might be stuff going on in there that's not needed. Let me know anything helps!

An example of what the program should output given different scenarios

Answer 1

You can trim down your code. There are variables that you don't require. Explanations after the code.

import java.util.Scanner;

public class GradeAvg {
    private static final int  SIZE = 10;

    public static void main(String[] args) {
        Scanner userIn = new Scanner(System.in);
        double[] grades = new double [SIZE];
        int counter = 0;
        String sTemp = "";
        double sum = 0;

        while(counter < SIZE) {
            System.out.println("Please enter grade " + (counter + 1) + ": ");
            sTemp = userIn.nextLine();
            if (sTemp.isEmpty()) {
                break;
            }
            try {
                grades[counter] = Double.parseDouble(sTemp);
            }
            catch (NumberFormatException xNumberFormat) {
                System.out.println("That wasn't a valid percentage, I need a number between 0 - 100. Try again.");
                continue;
            }
            if (grades[counter] < 0  ||  grades[counter] > 100) {
                System.out.println("That wasn't a valid percentage, I need a number between 0 - 100. Try again.");
                continue;
            }
            sum += grades[counter];
            counter++;
        } //end of while loop
        for (int i = 0; i < counter; i++) {
            System.out.println("grade " + (i + 1) + ": " + grades[i]);
        }
        System.out.println();
        System.out.println("number of valid grades entered: " + counter);
        System.out.println();
        System.out.println("average: " + sum / counter);
    }
}

After accepting the user input, first check if the user simply pressed <ENTER> without entering a value. I used method isEmpty() , of class java.lang.String , to do this check. If the user simply pressed <ENTER> , you need to exit the while loop. This is what break does. So no need for boolean variable exit .

Variable counter is all you need to both keep track of how many grades have been entered and which index of array grades needs to be assigned a value, so no need for variable counterList .

If an invalid value is entered, continue skips the rest of the while loop and starts a new loop iteration. Think of it as a sort of goto that jumps back to the statement:

while (counter < SIZE)

You can assign a value directly to an element in array grades so no need for variable gradeNum .

You can update variable sum inside the while loop so no need for the extra for loop in order to calculate the average. By the way, your calculation of the average is incorrect since you are dividing by the size of array grades and not by the actual number of grades that were entered. Adding up all the elements in array grades still gives you the correct sum since all elements of the array are implicitly initialized to 0 (zero).

I changed what the program displays on the screen so as to match your example of what the program should output given different scenarios .

Here is the output according to the sample you provided.

Please enter grade 1: 
A
That wasn't a valid percentage, I need a number between 0 - 100. Try again.
Please enter grade 1: 
100
Please enter grade 2: 
Bob
That wasn't a valid percentage, I need a number between 0 - 100. Try again.
Please enter grade 2: 
41.5
Please enter grade 3: 
-7
That wasn't a valid percentage, I need a number between 0 - 100. Try again.
Please enter grade 3: 

grade 1: 100.0
grade 2: 41.5

number of valid grades entered: 2

average: 70.75

Answer 2

I made some adjustments:

    final int SIZE = 10;
    Scanner userIn = new Scanner(System.in);
    double[] grades = new double [SIZE];
    int counter = 0;
    String sTemp = "";
    double gradeNum = 0;
    double sum = 0;
    
    while(counter < SIZE) {
        
        boolean err = false;
        System.out.println("Enter grade " + (counter + 1) +
                ", or press enter to quit.");
        sTemp = userIn.nextLine();
        
        try {
            gradeNum = Double.parseDouble(sTemp);
        } catch(NumberFormatException ex)
        { 
            err = true;
        }
        
        if(sTemp.length() < 1) {
            
            break; //ending the loop

            } else if(gradeNum <= 100 && gradeNum >= 0 && !err)
            {                   
                grades[counter] = gradeNum;
                counter++;
            } else
            {
                System.out.println("That wasn't a valid percentage, I need a number between 0 - 100. Try again.");
            }
    } //end of while loop
    userIn.close(); //closing the Scanner
      
    System.out.println("You entered " + counter + " grades total.");
    for(int i = 0; i < counter; i++) {
        
        System.out.println("Your grade " + (i + 1)+ " is " + grades[i]);
    }
    
    for(int i = 0; i < counter; i++) {
        
        sum += grades[i];
        
    }

    System.out.println("\nNumber of valid grades entered: " + counter + "\n");
    
    System.out.println("The average grade is: " + sum / counter);
    
}

This seems to work, I made some corrections (like SIZE declaration, took out the println from the last loop, replaced exit with a break statement, ...). The most relevant changes are the input checks and the average grade calculation (I used counter instead of grades.length because it is always 10). The try/catch checks if the input string contains only numbers.

(sorry for bad english, just ask if something isn't clear)