Question

The following C++ program is a slightly modified version of Program 5.20 from Gary J. Bronson textbook. In this program, you compute and display the average of three grades of each student for a class of four students. You need to modify the code to compute and display the class average as well as the standard deviation. Your code changes are as follows:

1. The variable “double grade” should be replaced by a two-dimensional array variable “double grade[NUMSTUDENTS][NUMGRADES].” Also replace the variable “double average” by “double average[NUMSTUDENTS].” This is necessary since you need to save the entered grades specially to compute the standard deviations.

2. After completing the display of the average grade of all students, your program should compute the class average (i.e., the average of four students’ average grades) and display.

3. Determine and display the class standard deviation by subtracting the class average from each student’s average grade (that results in a set of new numbers, each called a deviation); squaring each deviation; adding the squared deviations; dividing the sum by the number of students, NUMSTUDENTS; and taking its square root.

#include <iostream>

using namespace std;

int main()

{

const int NUMGRADES = 3;

const int NUMSTUDENTS = 4;

int i,j;

double grade, total, average;

for (i = 0; i < NUMSTUDENTS; i++) // start of outer loop

{

total = 0; // clear the total for this student

for (j = 0; j < NUMGRADES; j++) // start of inner loop

{

cout << "Enter an examination grade for this student: ";

cin >> grade;

total += grade; // add the grade into the total

} // end of the inner for loop

average = total / NUMGRADES; // calculate the average

cout << "\nThe average for student " << i << " is " << average << "\n\n";

} // end of the outer for loop

return 0;

}

Copy and paste your modified C++ code here:

Copy and paste display from the Console Debug window here:

Answer 1

#include <bits/stdc++.h>
using namespace std;

int main(){

    const int NUMGRADES = 3;
    const int NUMSTUDENTS = 4;

    int i,j;

    //double grade, total, average;
    double grade[NUMSTUDENTS][NUMGRADES];
    double average[NUMSTUDENTS];
    double total, classAverage = 0, standardDeviation = 0;
    
    for (i = 0; i < NUMSTUDENTS; i++) {
        
        total = 0;                             // clear the total for this student
        
        for (j = 0; j < NUMGRADES; j++) {
            
            cout << "Enter an examination grade for student " << i << ": ";
            cin >> grade[i][j];
            
            total += grade[i][j]; // add the grade into the total
        }
        average[i] = total / NUMGRADES; // calculate the average

        cout << "\nThe average for student " << i << " is " << average[i] << "\n\n";
    }
    
    for(i = 0; i < NUMSTUDENTS; i++) {
        classAverage += average[i];
    }
    
    classAverage /= NUMSTUDENTS;
    
    cout << "The Class Average is " << classAverage << "\n\n";
    
    
    //Standard Deviation calculation
    for(i = 0; i < NUMSTUDENTS; i++) {
        standardDeviation += (classAverage - average[i]) * (classAverage - average[i]);
    }
    
    standardDeviation /= NUMSTUDENTS;
    standardDeviation = sqrt(standardDeviation);

    cout << "The Standard Deviation is " << standardDeviation << "\n";
    
    return 0;
}

Output :-

Enter an examination grade for student 0: 15
Enter an examination grade for student 0: 65
Enter an examination grade for student 0: 28

The average for student 0 is 36

Enter an examination grade for student 1: 87
Enter an examination grade for student 1: 64
Enter an examination grade for student 1: 59

The average for student 1 is 70

Enter an examination grade for student 2: 35
Enter an examination grade for student 2: 84
Enter an examination grade for student 2: 34

The average for student 2 is 51

Enter an examination grade for student 3: 95
Enter an examination grade for student 3: 45
Enter an examination grade for student 3: 94

The average for student 3 is 78

The Class Average is 58.75

The Standard Deviation is 16.3917