Array to Determine Grades

[Rob Frank]

ok so i know this is wrong......very wrong. i obviously don't know whats going on here. i have a base array with an output of sum, average, largest test score and lowest test score that i created. i have to add a letter grade to these scores and how many scores are of that letter grade for example if a score above 90 gets entered 3 times it needs to say "the number of students with scores of 90-100 (A) is 3. so here is what i did....very wrong i know.

import javax.swing.JOptionPane;

public class ArrayProgram3 {

    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        for (int i = 0; i < scores.length; i++) {
            sum = sum + scores[i];
            if (scores[i] > largest) {
                largest = scores[i];
            }
            if (scores[i] < smallest) {
                smallest = scores[i];
            }
            int grades[] = new int[number];
            for (int f = 0; f < 60; f++) {
                for (int d = 0; d < 70; d++) {
                    for (int c = 0; c < 80; c++) {
                        for (int b = 0; b < 90; b++) {
                            for (int s = 0; s < 100; s++) {
                                if (grades[s] >= 90) {
                                    s = grades[s];
                                }
                                if (grades[b] >= 80 && grades[b] < 90) {
                                    b = grades[b];
                                }
                                if (grades[c] >= 70 && grades[b] < 80) {
                                    c = grades[c];
                                }
                                if (grades[d] >= 60 && grades[d] < 70) {
                                    d = grades[d];
                                } else {
                                    f = grades[f];
                                }

                                {

                                    //output
                                    JOptionPane.showMessageDialog(
                                            null, "The sum is " + sum
                                            + "\nThe average is " + sum / scores.length
                                            + "\nThe largest score is " + largest
                                            + "\nThe smallest score is " + smallest
                                            + "\nThe number of students with scores of 90-100 (A) is " + s
                                            + "\nThe number of students with scores of 80-89 (B) is " + b
                                            + "\nThe number of students with scores of 70-79 (C) is " + c
                                            + "\nThe number of students with scores of 60-69 (D) is " + d
                                            + "\nThe number of students with scores below 60 (F) is " + f);

                                }

                            }
                        }
                    }
                }
            }
        }
    }
}

here is what i built earlier and began to modify

import javax.swing.JOptionPane;

public class ArrayProgram3 {

    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        for (int i = 0; i < scores.length; i++) {
            sum = sum + scores[i];
            if (scores[i] > largest) {
                largest = scores[i];
            }
            if (scores[i] < smallest) {
                smallest = scores[i];
            }
        }
        //output
        JOptionPane.showMessageDialog(null, "The sum is " + sum
                + "\nThe average is " + sum / scores.length
                + "\nThe largest score is " + largest
                + "\nThe smallest score is " + smallest);

    }

}

i cant find any information on building an array to add up these numbers based on what numbers they are. couldn't find the correct way to search for it on the net and i don't believe my book goes over it.

again any help is very much appreciated.

Thanks,
Rob

[Rob Frank]

sorry i did something wrong with posting and i don't see an edit post button.

import javax.swing.JOptionPane; 

public class ArrayProgram3 { 

    public static void main(String[] args) { 
        // create array based on the number of args entered by user 
        String response = JOptionPane.showInputDialog(null, "Number of scores:"); 
        int number = Integer.parseInt(response); 
        int scores[] = new int[number]; 
        // for loop to convert String args array to integer myArray 
        for (int a = 0; a < number; a++) { 
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1)); 
            scores[a] = Integer.parseInt(response); 
        } 
        int sum = 0; 
        int largest = Integer.MIN_VALUE; 
        int smallest = Integer.MAX_VALUE; 
        //for loop to find sum, largest and smallest 
        for (int i = 0; i < scores.length; i++) { 
            sum = sum + scores[i]; 
            if (scores[i] > largest) { 
                largest = scores[i]; 
            } 
            if (scores[i] < smallest) { 
                smallest = scores[i]; 
            } 
            int grades[] = new int[number]; 
            for (int f = 0; f < 60; f++) { 
                for (int d = 0; d < 70; d++) { 
                    for (int c = 0; c < 80; c++) { 
                        for (int b = 0; b < 90; b++) { 
                            for (int s = 0; s < 100; s++) { 
                                if (grades[s] >= 90) { 
                                    s = grades[s]; 
                                } 
                                if (grades[b] >= 80 && grades[b] < 90) { 
                                    b = grades[b]; 
                                } 
                                if (grades[c] >= 70 && grades[b] < 80) { 
                                    c = grades[c]; 
                                } 
                                if (grades[d] >= 60 && grades[d] < 70) { 
                                    d = grades[d]; 
                                } else { 
                                    f = grades[f]; 
                                } 

                                { 

                                    //output 
                                    JOptionPane.showMessageDialog( 
                                            null, "The sum is " + sum 
                                            + "\nThe average is " + sum / scores.length 
                                            + "\nThe largest score is " + largest 
                                            + "\nThe smallest score is " + smallest 
                                            + "\nThe number of students with scores of 90-100 (A) is " + s 
                                            + "\nThe number of students with scores of 80-89 (B) is " + b 
                                            + "\nThe number of students with scores of 70-79 (C) is " + c 
                                            + "\nThe number of students with scores of 60-69 (D) is " + d 
                                            + "\nThe number of students with scores below 60 (F) is " + f); 

                                } 

                            } 
                        } 
                    } 
                } 
            } 
        } 
    } 
} 

and here is my original

import javax.swing.JOptionPane;

public class ArrayProgram3 {

    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        for (int i = 0; i < scores.length; i++) {
            sum = sum + scores[i];
            if (scores[i] > largest) {
                largest = scores[i];
            }
            if (scores[i] < smallest) {
                smallest = scores[i];
            }
        }
        //output
        JOptionPane.showMessageDialog(null, "The sum is " + sum
                + "\nThe average is " + sum / scores.length
                + "\nThe largest score is " + largest
                + "\nThe smallest score is " + smallest);

    }

}

[Carey Brown]

I see that you attempted to use Code tags. Two points for trying but they didn't go in quite right. I fixed it for you this time. You first need to highlight your block of code by dragging the mouse over it, then click the "Code" button. To verify that it worked correctly, click on the "Preview" button just below the edit window.

[Rob Frank]

lol i wondered how my original got fixed by the time i fixed it myself on the second post . thanks

[Piet Souris]

hi Rob,

as you will have noticed, this way is not very handy, to say the least... As soon as you get a new set of observations, you need to edit your main class.

So, a better way is to create a Statistics class. As soon as you have your observations, you instantiate this class, add the observations, and off you go.

To get you started, I made a simple Statistics class, to demonstrate how it could work. I used an ArrayList in stead of a fixed size array, so you don't need to know upfront how many observations to deal with.
I also used some handy java 8 methods, but if that is currently a brindge too far, then you can replace them by the means you have currently available. Here goes:

class Statistics {
    private final List<Double> observations = new ArrayList<>();
    
    public boolean addObervation(double d) {
        return observations.add(d);
    }
    
    public List<Double> getObservations() {
        return new ArrayList<>(observations);
    }
    
    public int count() {
        return observations.size();
    }
    
    public double average() {
        if (observations.isEmpty()) throw new RuntimeException("no observations");
        return observations.stream().mapToDouble(d -> d).sum() / count();
    }
    
    public double variance() {
        if (observations.size() < 2) throw new RuntimeException("not enough observations");
        double Ex2 = observations.stream().mapToDouble(d -> d * d).sum() / count();
        double avg = average();
        return Ex2 - avg * avg;
    }
    
    public double min() {
        if (observations.isEmpty()) throw new RuntimeException("No observations");
        return observations.stream().min(Comparator.naturalOrder()).get();
    }
    
    public static String grade(double observation) {
        if (observation > 90) return "A";
        else if (observation > 80) return "B";
        // etcetera
        return "F";
    }
    
    public Map<String, Long> getFrequencyOfGrades() {
        Map<String, Long> map = observations.stream().collect(Collectors.groupingBy(Statistics::grade, Collectors.counting()));
        return map;
    }
}

[Rob Frank]

hey thanks. i'll work with that tonight after work and see how it goes. i will say that using throw new runtimeextension was not covered at all in this class so i will stay away from that for now.

[Rob Frank]

ok so i tried playing with that a little bit but i have to ask. could you dumb that down for me.  i know that i can't use the throw new and runtime exception because that wasn't covered in my course but i know how to replace that. but the variables ArrayList and List i'm not sure what do with. I've only had practice with using an array on the last couple assignments and they were simple and actually spelled out. to see the level of difficulty of the previous assignments my original i have posted is the last assignment that i've done that i'm trying to modify. i'm so frustrated that i get assignments like this that seem so simple to others and i have to beat my head off the desk because this material wasn't covered.

[Carey Brown]

I myself use the Statistics class approach, however I feel that that is above your experience level and your requirements can be achieved with some minor additions to your original code.

import javax.swing.JOptionPane;
 
public class ArrayProgram3 {
 
    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        int countA = 0; // *******************
        ...

        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        for (int i = 0; i < scores.length; i++) {
            sum = sum + scores[i];
            if (scores[i] > largest) {
                largest = scores[i];
            }
            if (scores[i] < smallest) {
                smallest = scores[i];
            }

            // ******************
            if( scores[i] >= 90 ) {
                countA++;
            }
            else if( scores[i] >= 80 ) {
                countB++;
            }
            ...
        }
        //output
        JOptionPane.showMessageDialog(null, "The sum is " + sum
                + "\nThe average is " + sum / scores.length
                + "\nThe largest score is " + largest
                + "\nThe smallest score is " + smallest);
 
    }
 
}

[Noorul Hameed]

Dear Mr. Rob Frank,

Variable have to initialized before its implementation:
So, I have corrected your end of source part as show in below:

// ******************
                int countA=0, countB=0, countC=0, countD=0, countF=0;
	  if (scores[i] >= 90) { 
                                   countA++;
                                }else if (scores[i] >= 80 && scores[i] < 90) { 
                                   countB++;
                                }else if (scores[i] >= 70 && scores[i] < 80) { 
                                   countC++;
                                }else if (scores[i] >= 60 && scores[i] < 70) { 
                                   countD++;
                                } else { 
                                   countF++;
                                } 
 
        }
        //output
        JOptionPane.showMessageDialog(null, "The sum is " + sum
                + "\nThe average is " + sum / scores.length
                + "\nThe largest score is " + largest
		+ "\nThe smallest score is " + smallest 
                + "\nThe number of students with scores of 90-100 (A) is " + countA
                + "\nThe number of students with scores of 80-89 (B) is " + countB 
                + "\nThe number of students with scores of 70-79 (C) is " + countC 
                + "\nThe number of students with scores of 60-69 (D) is " + countD 
                + "\nThe number of students with scores below 60 (F) is " + countF); 

Thanks

Regards
Dr. Noorul

[Carey Brown]

Not that by using "else if" you no longer need the "&&" component because that is taken care of by the order that these comparisons are made.

		if( scores[i] >= 90 ) {
			countA++;
		} else if( scores[i] >= 80 ) {
			countB++;
		} else if( scores[i] >= 70 ) {
			countC++;
		} else if( scores[i] >= 60 ) {
			countD++;
		} else {
			countF++;
		}

[Rob Frank]

ok so if i get all that going it works but if i enter 5 scores i have to click 5 times and i see my letter grades appear 1 by 1 and the sum and average also go up 1 at a time. my loop is not looping back before displaying the final joptionpane. i'm not sure if i need to change the for loop or if i need a return statement. i tried using a return statement a couple different ways and either got an error or the program just doesn't run (visually) and says build complete.

import javax.swing.JOptionPane;

public class ArrayProgram3 {

    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        int countA = 0, countB = 0, countC = 0, countD = 0, countF = 0;
        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        for (int i = 0; i < scores.length; i++) {
            sum = sum + scores[i];
            if (scores[i] > largest) {
                largest = scores[i];
            }
            if (scores[i] < smallest) {
                smallest = scores[i];
            }
            if (scores[i] >= 90) {
                countA++;
            } else if (scores[i] >= 80) {
                countB++;
            } else if (scores[i] >= 70) {
                countC++;
            } else if (scores[i] >= 60) {
                countD++;

            } else {
                countF++;
            }// DO I NEED A RETURN STATEMENT HERE SOMEHOW? WHAT VARIABLE DO I CALL ON??
            //output
            JOptionPane.showMessageDialog(null, "The sum is " + sum
                    + "\nThe average is " + sum / scores.length
                    + "\nThe largest score is " + largest
                    + "\nThe smallest score is " + smallest
                    + "\nThe number of students with scores of 90-100 (A) is "
                    + countA
                    + "\nThe number of students with scores of 80-89 (B) is "
                    + countB
                    + "\nThe number of students with scores of 70-79 (C) is "
                    + countC
                    + "\nThe number of students with scores of 60-69 (D) is "
                    + countD
                    + "\nThe number of students with scores below 60 (F) is "
                    + countF);

        }

    }
}

[Prasad Saya]

ok so if i get all that going it works but if i enter 5 scores i have to click 5 times and i see my letter grades appear 1 by 1 and the sum and average also go up 1 at a time.
my loop is not looping back before displaying the final joptionpane.

I ran the program. What do you mean by "my loop is not looping back before displaying the final joptionpane."?

i'm not sure if i need to change the for loop or if i need a return statement. i tried using a return statement a couple different ways and either got an error or the program just doesn't run (visually) and says build complete.

This is not clear to me.

What is it the program is not doing and what is the expectation.

[Noorul Hameed]

Hi,

The problem is to close the for loop befor last statement, JOptionPane...

It can not be inside the loop. It is after for loop completed.

Thanks
Regards
Dr.Noor

[Prasad Saya]

Noorul Hameed wrote:Hi, The problem is to close the for loop befor last statement, JOptionPane...It can not be inside the loop. It is after for loop completed.
Thanks
Regards
Dr.Noor

I get it, thanks.

[Campbell Ritchie]

Carey Brown wrote:Not that by using "else if" you no longer need the "&&" component because that is taken care of by the order that these comparisons are made.

		if( scores[i] >= 90 ) {
			countA++;
		} else if( scores[i] >= 80 ) {
			countB++;
		} else if( scores[i] >= 70 ) {
			countC++;
		} else if( scores[i] >= 60 ) {
			countD++;
		} else {
			countF++;
		}

Anther thing about else‑if. If your boundary value is included in the upper category, start small. The boundary value for a C is 70, and 70 is included in the C grade, not the D grade. If you start small, you don't need >=, but <. The >= and <= operators aren't actually bad, but < and > are easier to understand.

		if( scores[i] < 60 ) {  //start with small scores
			countF++;
		} else if( scores[i] < 70 ) {
			countD++;
		} else if( scores[i] < 80 ) {
			countC++;
		} else if( scores[i] < 90 ) {
			countB++;
		} else { // finish with large scores
			countA++;
		}

When you write that sort of thing always keep the terms in order, ascending or descending. You might so well to precede that if with something like

if (score < 0 || score > 100)
{
   throw new IllegalArgumentException(
         "Scores only permissible between 0 and 100.");
} // else not required at this stage.

Remember it is usually not a good idea to write lots of number literals like that, but that is a different problem.

[Rob Frank]

ok so all you guys are great. i was able to get this going. had to play around with adding a "do while" loop so i just get one output at the end. here it is. I still can't use the throw new because my material doesn't cover that and i'm trying to stay away from adding things that i really shouldn't know to my code. so on that note i'm trying to add a return for line 13

import javax.swing.JOptionPane;

public class ArrayProgram3 {

    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        int countA = 0, countB = 0, countC = 0, countD = 0, countF = 0;
        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
            if (scores[a] < 0 || scores[a] > 100) {
                JOptionPane.showMessageDialog(null, "Scores only permissible"
                        + "between 0 and 100 " );
                // I WOULD LIKE TO MAKE A RETURN TO RESPONSE HERE I CANNOT FIGURE OUT HOW
            }
        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        do {
            for (int i = 0; i < scores.length; i++) {
                sum = sum + scores[i];
                if (scores[i] > largest) {
                    largest = scores[i];
                }
                if (scores[i] < smallest) {
                    smallest = scores[i];
                }
                if (scores[i] < 60) {
                    countF++;
                } else if (scores[i] < 70) {
                    countD++;
                } else if (scores[i] < 80) {
                    countC++;
                } else if (scores[i] < 90) {
                    countB++;

                } else {
                    countA++;
                }
            }
        } while (countA + countB + countC + countD + countF < scores.length);
        // I FIGURED OUT THIS WHILE LOOP AND NOW THE PROGRAM WORKS HOW I NEED IT
        //output
        JOptionPane.showMessageDialog(null, "The sum is " + sum
                + "\nThe average is " + sum / scores.length
                + "\nThe largest score is " + largest
                + "\nThe smallest score is " + smallest
                + "\nThe number of students with scores of 90-100 (A) is "
                + countA
                + "\nThe number of students with scores of 80-89 (B) is "
                + countB
                + "\nThe number of students with scores of 70-79 (C) is "
                + countC
                + "\nThe number of students with scores of 60-69 (D) is "
                + countD
                + "\nThe number of students with scores below 60 (F) is "
                + countF);
    }

}

[Rob Frank]

I'm trying to do this
it obviously doesn't work.

String message = JOptionPane.showMessageDialog (null;("Scores only permissible"
                        + "between 0 and 100 " );
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
            if (scores[a] < 0 || scores[a] > 100) {
                return message;

[Noorul Hameed]

Campbell Ritchie wrote:

Carey Brown wrote:

Hi Mr. Rob
This task has already been explored by Mr Cambell Richie. Please have a look at quote here.
something like

if (score < 0 || score > 100)
{
   throw new IllegalArgumentException(
         "Scores only permissible between 0 and 100.");
} // else not required at this stage.

Remember it is usually not a good idea to write lots of number literals like that, but that is a different problem.

Thanks.

[Prasad Saya]

Rob Frank wrote:I'm trying to do this
it obviously doesn't work.

String message = JOptionPane.showMessageDialog (null;("Scores only permissible"
                        + "between 0 and 100 " );
        for (int a = 0; a < number; a++) {
            response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
            scores[a] = Integer.parseInt(response);
            if (scores[a] < 0 || scores[a] > 100) {
                return message;

Try this code. This loops until the valid scores are entered:

for (int a = 0; a < number; a++) {
    VALID_SCORE_LOOP:
    do {
        response = JOptionPane.showInputDialog(null, "Enter score" + (a + 1));
        scores[a] = Integer.parseInt(response);
        if (scores[a] < 0 || scores[a] > 100) {
            JOptionPane.showMessageDialog(null, "Scores only permissible"
                   + "between 0 and 100 " );
            continue VALID_SCORE_LOOP;
        }
        break VALID_SCORE_LOOP;
    } while (true);
} // end for-loop

Note the VALID_SCORE_LOOP is called as a loop label. And, this can also be used with for-loops.

[Rob Frank]

ok its put together and everything works great. i cant enter anything to make the program not work correctly so i'm thrilled. just to let anyone know because it seems like i'm asking stupid questions and i'm telling you i can't use certain items because they weren't in my course. this is my final project (not worth a lot of points or anything but it is my last assignment) i've only asked for help on this one and the one previous. i should finish this class with over %100. so if you can imagine i'm having trouble with this that means everything else i've done has been so simple its stupid and it obviously didn't teach me enough. a few of you have taught me alot with just a few lines of code. I really appreciate it.

import javax.swing.JOptionPane;

public class ArrayProgram3 {

    public static void main(String[] args) {
        // create array based on the number of args entered by user
        String response = JOptionPane.showInputDialog(null, "Number of scores:");
        int number = Integer.parseInt(response);
        int scores[] = new int[number];
        // set variables for letter grade counting
        int countA = 0, countB = 0, countC = 0, countD = 0, countF = 0;
        // for loop to convert String args array to integer myArray
        for (int a = 0; a < number; a++) {
        // user enters scores
            do {
                response = JOptionPane.showInputDialog(null, "Enter score"
                        + (a + 1));
                scores[a] = Integer.parseInt(response);
                // if loop to have user re enter score if it is a invalid number
                if (scores[a] < 0 || scores[a] > 100) {
                    JOptionPane.showMessageDialog(null, "Scores only permissible"
                            + "between 0 and 100 ");
                    continue;
                }
                break;
            } while (true);
            // end for-loop

        }
        int sum = 0;
        int largest = Integer.MIN_VALUE;
        int smallest = Integer.MAX_VALUE;
        //for loop to find sum, largest and smallest
        // do while loop to loop back and add all letter grades correctly 
        do {
            for (int i = 0; i < scores.length; i++) {
                sum = sum + scores[i];
                if (scores[i] > largest) {
                    largest = scores[i];
                }
                if (scores[i] < smallest) {
                    smallest = scores[i];
                }
                if (scores[i] < 60) {
                    countF++;
                } else if (scores[i] < 70) {
                    countD++;
                } else if (scores[i] < 80) {
                    countC++;
                } else if (scores[i] < 90) {
                    countB++;

                } else {
                    countA++;
                }
            }
        } while (countA + countB + countC + countD + countF < scores.length);
        //output
        JOptionPane.showMessageDialog(null, "The sum is " + sum
                + "\nThe average is " + sum / scores.length
                + "\nThe largest score is " + largest
                + "\nThe smallest score is " + smallest
                + "\nThe number of students with scores of 90-100 (A) is "
                + countA
                + "\nThe number of students with scores of 80-89 (B) is "
                + countB
                + "\nThe number of students with scores of 70-79 (C) is "
                + countC
                + "\nThe number of students with scores of 60-69 (D) is "
                + countD
                + "\nThe number of students with scores below 60 (F) is "
                + countF);
    }

}

[Knute Snortum]

I don't know if it's in the scope of your project, but I can easily crash your program by entering letters instead of numbers.  Do you need error processing?

[Rob Frank]

you are correct it does crash when a letter is entered. although i do not think its required at all to actually fix that for this assignment i am very curious on how you do that. i tried to change my statement to something like if scores != Integer and other things like that and it doesn't even come close to working or really giving me any other ideas.

[Rob Frank]

i'm also wondering if count A , B, C, D and F can be made into an array. i'm done being stressed about this now so i would actually like to spend some time with this program and learn.

[Campbell Ritchie]

Rob Frank wrote:i'm also wondering if count A , B, C, D and F can be made into an array. . . .

Of course they can. But I can see problems lining up the grades and the numbers in the array.

[Carey Brown]

You don't need your
do { ... } while (countA + countB + countC + countD + countF < scores.length);
Your for() loop already deals with that. The problem you were having before was that your showMessageDialog() needed to be outside the for() loop.

To use an array for the counters

        String[] gradeLetters = { "A", "B", "C", "D", "F" };
        int[] minScoresPerGrade = {  90, 80, 70, 60,  0 };
        int[] maxScoresPerGrade = { 100, 89, 79, 69, 59 };
        int[] counters = new int[ 5 ];

...
		for( int i = 0 ; i < scores.length ; i++ ) {
			sum = sum + scores[i];
			if( scores[i] > largest ) {
				largest = scores[i];
			}
			if( scores[i] < smallest ) {
				smallest = scores[i];
			}

			for( int j = 0 ; j < 5 ; j++ ) {
				if( scores[i] >= minScoresPerGrade[j] ) {
					counters[j]++;
					break;
				}
			}
		}
...
        StringBuilder sb = new StringBuilder();
        for( int j=0 ; j < 5 ; j++ ) {
        	sb.append( String.format(
        		"\nThe number of students with scores of %d-%d (%s) is %d",
        			minScoresPerGrade[j],
        			maxScoresPerGrade[j],
        			gradeLetters[j],
        			counters[j] ) );
        }
            
        JOptionPane.showMessageDialog( null, "The sum is " + sum
        		+ "\nThe average is " + sum / scores.length
        		+ "\nThe largest score is " + largest
        		+ "\nThe smallest score is " + smallest
        		+ sb.toString() );
    }

Seeing as how you only have 5 grades, I don't see that this buys you much, but it is interesting from a coding standpoint.

[Piet Souris]

Let's "dumb" the class I gave. Mind you, the story goes that with java 8 you only need to tell java what to do, and it decides for itself how to do it, while with previous java versions, you must also tell how to do it. Well, that's the story, and if true, we are not "dumbing" it, but making it more difficult....

So, here is the dumbed version, that now uses an array, and has a constructor that takes an array of observations as parameter.

class Statistics {
    
    private final double[] observations;
    
    Statistics(double[] obs) {
        observations = obs;
    }
    
    public double min() {
        double d = observations[0];
        for (int index = 1; index < observations.length; index++) {
            if (observations[index] < d) d = observations[index];
        }
        return d;
    }
    
    public double max() {
        return 0;  // hmm, code could be improved a little
    }
    
    public double average() {
        double total = 0;
        for (int index = 0; index < observations.length; index++) total += observations[index];
        return total / observations.length;
    }
    
    public int[] grades() {
        // this is just a demo, real code has been shown in the replies so far
        int[] result = new int[6];  // for grades A t/m F
        result[0] = 5;
        result[1] = 7;
        // et cetera
        return result; 
    }
    
    @Override
    public String toString() {
        int[] grades = grades();
        String s1 = "observations: " + observations.length;
        String s2 = "average = " + average();
        String s3 = "min = " + min();
        String s4 = "nr of A = " + grades[0];
        String s5 = "nr of B = " + grades[1];
        return s1 + "\n" + s2 + "\n" + s3 + "\n" + s4 + "\n" + s5;
    }
}

Now, suppose you are qiven the results of two groups of students, groupA and groupB, with the question to compare both results on average, min, max, variance and grades frequency. You could now do it like this:

public class RobFrank {
    public static void main(String... args) {
        double[] resultsOfClassA = {30, 40, 50, 60};
        double[] resultsOfClassB = {70.5, 81.4, 55.0, 98.1, 33.6};
        Statistics classA = new Statistics(resultsOfClassA);
        Statistics classB = new Statistics(resultsOfClassB);
        System.out.println(classA);  // or use showMessageDialog
        System.out.println("***********");
        System.out.println(classB);
    }
}

You see that the method 'grades' returns an array, representing the frequencies of A, B et cetera. Ahead of schedule, compare this to what I did to get the frequencies with java 8: just one line of code!

And also: inputting an array via JOptionPane is not easy, as you noticed. It is far easier to make some files in this format:
73.4
80.8
91.6
30.20

and read these files in your code (if that subject has been taught yet). Well, I hope the advantages of a Statistics class are clear. It just lets you focus on the methods that you want, without getting a large inflexible main method. So, if you want things like curtosis or some sample from some distribution, you only need to adapt that class.

[Carey Brown]

Here's a refactored version. This encapsulates the GradeStatistics into its own class, similar to Piet's. It also uses an enum for a Grade. The Grade ordinal can be used as an index into a counts array. It uses an array of counts, one for each grade. The logic of entering and verifying a score has been moved from main() to its own method.

The overall number of lines of  code is a bit more but there is more encapsulation of responsibilities. Note how tiny main() has become and therefore much easier  to follow. Grade and GradeStatics could potentially be used in another project. It is also now possible to have multiple instances of GradStatistics going at the same time.

 import javax.swing.JOptionPane;

public class ArrayProgram4 {

	public static void main(String[] args) {
		String response = JOptionPane.showInputDialog( null,
				"Number of scores:" );
		int number = Integer.parseInt( response );
		int scores[] = new int[number];

		for( int a = 0 ; a < number ; a++ ) {
			scores[a] = enterScore( a );
		}

		GradeStatistics stats = new GradeStatistics();

		for( int score : scores ) {
			stats.add( score );
		}

		JOptionPane.showMessageDialog( null, stats.toString() );
	}

	private static int enterScore( int a ) {
		while( true ) {
			String response = JOptionPane.showInputDialog( null,
					"Enter score " + ( a + 1 ) );
			try {
				int score = Integer.parseInt( response );
				if( score >= 0 && score <= 100 )
					return score;
			}
			catch( Exception ex ) {
			}
			JOptionPane.showMessageDialog( null,
					"Scores only permissible between 0 and 100 " );
		}
	}
}

//======================================================================
enum Grade
{
	A(90,100),
	B(80,89),
	C(70,79),
	D(60,69),
	F(0,59);

	private static Grade[] grades = values();

	int			min;
	int			max;

	private Grade( int min, int max ) {
		this.min = min;
		this.max = max;
	}

	public static int getMin( int ordinal ) {
		return grades[ordinal].min;
	}

	public static String getDescription( int ordinal ) {
		Grade g = grades[ordinal];
		return String.format( "%d-%d (%s)", g.min, g.max, g );
	}
}

//======================================================================
class GradeStatistics
{
	private int sum = 0;
	private int count = 0;
	private int max = Integer.MIN_VALUE;
	private int min = Integer.MAX_VALUE;
	private int[] counters = new int[ 5 ];

	public void add( int grade ) {
		sum += grade;
		count++;
		if( grade > max )
			max = grade;
		if( grade < min )
			min = grade;
		for( int j = 0 ; j < 5 ; j++ ) {
			if( grade >= Grade.getMin( j ) ) {
				counters[j]++;
				break;
			}
		}
	}

	public String getGradeStats( int i ) {
		return String.format( "The number of students with a score of %s is %d",
				Grade.getDescription( i ), counters[i] );
	}

	public String toString()
	{
		StringBuilder sb = new StringBuilder();
		sb.append( "The sum is " + getSum() );
		sb.append( "\nThe average is " + getAverage() );
		sb.append( "\nThe highest score is " + getMax() );
		sb.append( "\nThe lowest score is " + getMin() );
		
		for( int j = 0 ; j < 5 ; j++ ) {
			sb.append( "\n" ).append( getGradeStats( j ) );
		}

		return sb.toString();
	}
	
	public int getAverage() {
		return sum / count;
	}

	public int getSum() {
		return sum;
	}

	public int getMin() {
		return min;
	}

	public int getMax() {
		return max;
	}
}

[Rob Frank]

this is all really good stuff. i can see how only knowing how to do a few things with java can really complicate the code. not sure learning how to complicate the code should be in a beginning java class. anyways i removed my do while loop for the count and added a brace to move my output outside the loop. that did correct it and the program works fine. at this point it looks like the program functions the way it should and only includes items that i have gone over in this class.  and building the array using joptionpane wasn't something i came up with. that was the program i was instructed to build previously and had to work off of that. yes i see that it again complicates things.  i do think that if i take another java class i'll invest in a real book. the required book for this class was alice 3 with java and while alice 3 is "fun" i didn't find it very useful in taking up so many pages in the book and not going over enough actual coding.

[Carey Brown]

I'm glad you were successful. As you can see as a thread on this forum gets past the stage where the original poster has (mostly) succeeded other people tend to chime in with their own refactorizations using various features of Java that may not be in-scope for the OP but it does help to stretch the OP's knowledge.

Congrats.

[Carey Brown]

I might still suggest making an enterScore() method and get some of that mess out of main(). Data entry and validation usually requires their own methods in order to keep the calling methods cleaner and possibly yielding some reuseability.

[Piet Souris]

Rob Frank wrote:(...) i can see how only knowing how to do a few things with java can really complicate the code. not sure learning how to complicate the code should be in a beginning java class. anyways

The problem with java 8 is that the way to describe what must be done is often pretty complicated, taking quite some time to master. Being used to ways used in previous versions you may well find it a lot easier dong it the pre java 8 way...  Java does not always come easy.

[Rob Frank]

well other people posting what they think is the correct way is very useful even if i don't use it. it is a great way for me to see how things can be used and work. i should have became a member of this site a while ago. even though i didn't have that much trouble with previous assignments allowing other users to input their ideas would have really broadened my knowledge of using java. once again thanks to all that have replied. and thanks to you guys this assignment isn't graded yet but i'm sure i will get a good score on it and should finish with over 100 percent with the extra credit i'm due on some previous projects.

[Knute Snortum]

Here's my take on how to get an integer.  My getInt() is reuseable.  I use scan.nextLine() and Integer.parseInt() to give me a little more control, although it's not necessary in this situation.  You can also pass the prompt into getInt() or have a default value that gets set if you enter just an <enter> if you want to add that.

package net.snortum.play;

import java.util.Scanner;

public class InputInt {
	Scanner scan = new Scanner(System.in);

	public static void main(String[] args) {
		new InputInt().run();
	}

	private void run() {
		int grade;
		do {
			System.out.print("Enter grade (0 - 100): ");
			grade = getInt();
		} while (grade < 0 || grade > 100);
		
		System.out.println("Grade is " + grade);
	}

	private int getInt() {
		int result = 0;
		boolean needsAnother = true;
		
		do {
			String input = scan.nextLine();
			try {
				result = Integer.parseInt(input);
				needsAnother = false;
			} catch (Exception e) {
				System.out.println("Not an integer, try again");
				needsAnother = true;
			}
		} while (needsAnother);
		
		return result;
	}
}

[Campbell Ritchie]

I think there are easier ways to get an int, using the trick Rob Spoor taught me a long time ago:-

/**
 * .....
 */
public class KeyboardInputs
{
   private static final Scanner scan = new Scanner(System.in);

   private KeyboardInputs()
   {
      throw new UnsupportedOperationException(
            "Please don\u2019t use this constructor.");
   }

   /**
    * .....
    */
   public static int getInt(String prompt)
   {
      System.out.print(prompt);
      while (!scan.hasNextInt())
      {
         System.out.print("Incorrect input: int required: please try again: ");
         scan.next(); // necessary to discard current token
      }
      return scan.nextInt();
   }
   // ...
}

That method can be overloaded to print a custom error message, or to constrain the input to a predefined range. No need for any exceptions. The \u2019 Unicode character is a posh apostrophe ’.

[Knute Snortum]

That's a cool little method.

[Piet Souris]

Not sure whether this iopic is about getting some decent statistics, or getting an int from the keyboatd: as I remarked before, in real life the number of observations will be such that inputting these according to the methods mentioned, will be awkward. A  better way is to type the observations into NotePad or such, save it, and read the file into the code, even if that involves some extra java to learn.