C++ for-loop, while-loop and do-while-loop

[qingquan-li]

Assignment: Write a program to ask the user to enter students' grades and then calculate the total grade.

1. for loop:

#include <iostream>

using namespace std;

int main() {
    int num_students;
    float stu_grade; // student's numeric course grade
    float total_grade = 0;

    cout << "How many students are in the class? ";
    cin >> num_students;

    for (int i = 1; i <= num_students; i++) {
        cout << "Please enter the #" << i << " student's numeric course grade: ";
        cin >> stu_grade;
        total_grade += stu_grade;
    }

    cout << "The total grade of the class is: " << total_grade << endl;

    return 0;
}

2. while loop:

#include <iostream>

using namespace std;

int main() {
    const int SENTINEL_VAL = -1;
    float stu_grade; // student's numeric course grade
    float total_grade = 0;

    cout << "Type a student's numeric course grade (type -1 if you don't have any more grade): ";
    cin >> stu_grade;

    while (stu_grade != SENTINEL_VAL) {
        total_grade += stu_grade;
        cout << "Type a student's numeric course grade (type -1 if you don't have any more grade): ";
        cin >> stu_grade;
        // total_grade += stu_grade; // should at the beginning, otherwise, the -1 will be add.
    }

    cout << "The total grade of the class is: " << total_grade << endl;

    return 0;
}

3. do while loop:

#include <iostream>

using namespace std;

int main() {
    char user_response;
    float stu_grade; // student's numeric course grade
    float total_grade = 0;

    do {
        cout << "Type a student's numeric course grade: ";
        cin >> stu_grade;
        total_grade += stu_grade;
        cout << "Do you have another grade to type? (Y/N) ";
        cin >> user_response;
    } while (user_response == 'Y' || user_response == 'y');

    cout << "The total grade of the class is: " << total_grade << endl;

    return 0;
}