Question

Write an application that allows a user to enter any number of student quiz scores until the user enters 99. If the score entered is less than 0 or more than 10, display an appropriate message and do not use the score. After all the scores have been entered, display the number of scores entered, the highest score, the lowest score, and the arithmetic average. Save the file as QuizScoreStatistics.java.

I am struggling with looping in Java and do not understand how to go about it. Could someone help answer this and place cmments in the code?

Answer 1

import java.util.*; 

class Main {
public static void main(String[] args) {
    // We will use ArrayLists to store the data we have since the size of the data is not known. 
    ArrayList<Integer> marks = new ArrayList<Integer>(); 
    // We need a scanner object to get the input values from the user. 
    Scanner myObj = new Scanner(System.in);
    // This is a special loop used when the data is not known beforehand - that is, we do not know 
    // whether it's 10 or 100 values that are going to be stored. Hence, we use a while(true) loop 
    // And then we use a break statement on the condition that the input value is 99 as desired in the 
    // question. 
    while(true) {
    // we get the grades from the user 
      int grade = myObj.nextInt();
    // if it is a 99 value we need to terminate the loop - we use a "break" statement. 
      if(grade == 99) break;
    // When the grade entered does not match the condition of being between 0 and 10
    // We keep the loop running by terminating this instance of a loop 
    // and keeping the loop running anyway. We use a continue statement to accomplish this.  
      if(grade < 0 || grade > 10) {
        System.out.println("You have entered incorrect grade. Try again.");
        continue; 
      }
     // if the grade is a legal value we add it to the ArrayList 
      marks.add(grade);
    }
   // Now we get to the output statements. 
    System.out.print("You have entered data for ");
    System.out.print(marks.size());
    System.out.print(" students. \n");
   // We have not yet calculated the maximum and minimum values, we use for loops to accomplish this. 
   // If we encounter any value larger than the defined max_val, we update the max_val to that value. 
   // The reverse logic is applied for the min_val. 
   // Meanwhile we use a variable sum to keep track of the sum of all the elements so far. 
   // This is necessary to compute the average. 
    int max_val = marks.get(0);
    int min_val = marks.get(0); 
    int sum = 0; 
    for (int i = 0; i < marks.size(); i++) {
      if(marks.get(i) > max_val) max_val = marks.get(i); 
      if(marks.get(i) < min_val) min_val = marks.get(i);
      sum += marks.get(i);
    } 
    // Now we can compute the average since we have the sum of all elements as well as the 
    // total number of elements in the ArrayList. We get: 
    float avg = (int) sum/marks.size();
    System.out.print("The minimum score is ");
    System.out.print(min_val);
    System.out.print("\n");

    System.out.print("The maximum score is ");
    System.out.print(max_val);
    System.out.print("\n");

    System.out.print("The average score is ");
    System.out.print(avg);
    System.out.print("\n"); 
    
   // We now close the scanner to avoid resource leaks. 
    myObj.close();
  }
}

We have used ArrayList as the data structure to keep track of all the incoming values since we do not know the size beforehand (the user may enter as many values as they desire). The code has been commented with all the information necessary to understand the working of the code. A note:

This kind of program (where the user terminates and that decides the number of elements we need to store) requires a while(true) kind of looping structure. Here, we could have an arbitrarily large termination of a for loop, but this is a much more efficient way of achieving the same thing. We do not need to arbitrarily guess what would be the maximum number of iterations in this case. The break statement can terminate the loop whenever the desired condition is satisfied - in this case, that condition is satisfied when the value of the user input hits 99. Then we break out of the loop.

Another tricky usage here is of the continue statement - here, we notice that having one negative value or value greater than 10 does not mean we need to terminate the program, we merely need to skip it. Hence, again making use of the while(true) looping mechanism, we simply add a continue statement here so that the program can simply display an error message but continue executing anyway.

A sample run of the code here:

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