Two dimensional array

using System;  // Import the System namespace for basic functionality

class Program  // Define the main class
{
    static void Main()  // The entry point of the program
    {
        // Create a two-dimensional array to store marks for 2 groups of 10 pupils
        double[,] marks = new double[2, 10];  
        double group1Sum = 0, group2Sum = 0;  // Variables to store the sum of marks for each group
        double group1Average, group2Average;  // Variables to store the average marks for each group
        
        // Ask the user to enter marks for the pupils
        Console.WriteLine("Enter marks for 20 pupils (2 groups of 10):");
        
        // Input marks for Group 1 (10 pupils)
        for (int i = 0; i < 10; i++)
        {
            Console.Write($"Enter mark for pupil {i + 1} in Group 1: ");
            while (!double.TryParse(Console.ReadLine(), out marks[0, i]) || marks[0, i] < 0)
            {
                Console.WriteLine("Invalid input. Please enter a valid mark (non-negative number).");
                Console.Write($"Enter mark for pupil {i + 1} in Group 1: ");
            }
            group1Sum += marks[0, i];  // Add the mark to the sum for Group 1
        }

        // Input marks for Group 2 (10 pupils)
        for (int i = 0; i < 10; i++)
        {
            Console.Write($"Enter mark for pupil {i + 1} in Group 2: ");
            while (!double.TryParse(Console.ReadLine(), out marks[1, i]) || marks[1, i] < 0)
            {
                Console.WriteLine("Invalid input. Please enter a valid mark (non-negative number).");
                Console.Write($"Enter mark for pupil {i + 1} in Group 2: ");
            }
            group2Sum += marks[1, i];  // Add the mark to the sum for Group 2
        }

        // Calculate the average marks for each group
        group1Average = group1Sum / 10;
        group2Average = group2Sum / 10;

        // Display the averages for each group
        Console.WriteLine($"\nAverage mark for Group 1: {group1Average:F2}");
        Console.WriteLine($"Average mark for Group 2: {group2Average:F2}");
    }
}

 Output

Case 1:
Enter marks for 20 pupils (2 groups of 10):
Enter mark for pupil 1 in Group 1: 85
Enter mark for pupil 2 in Group 1: 90
Enter mark for pupil 3 in Group 1: 78
Enter mark for pupil 4 in Group 1: 88
Enter mark for pupil 5 in Group 1: 92
Enter mark for pupil 6 in Group 1: 79
Enter mark for pupil 7 in Group 1: 84
Enter mark for pupil 8 in Group 1: 95
Enter mark for pupil 9 in Group 1: 87
Enter mark for pupil 10 in Group 1: 91
Enter mark for pupil 1 in Group 2: 76
Enter mark for pupil 2 in Group 2: 83
Enter mark for pupil 3 in Group 2: 88
Enter mark for pupil 4 in Group 2: 78
Enter mark for pupil 5 in Group 2: 92
Enter mark for pupil 6 in Group 2: 85
Enter mark for pupil 7 in Group 2: 90
Enter mark for pupil 8 in Group 2: 81
Enter mark for pupil 9 in Group 2: 89
Enter mark for pupil 10 in Group 2: 80

Average mark for Group 1: 86.40
Average mark for Group 2: 84.30

Case 2:
Enter marks for 20 pupils (2 groups of 10):
Enter mark for pupil 1 in Group 1: 60
Enter mark for pupil 2 in Group 1: 75
Enter mark for pupil 3 in Group 1: 67
Enter mark for pupil 4 in Group 1: 80
Enter mark for pupil 5 in Group 1: 85
Enter mark for pupil 6 in Group 1: 90
Enter mark for pupil 7 in Group 1: 78
Enter mark for pupil 8 in Group 1: 88
Enter mark for pupil 9 in Group 1: 65
Enter mark for pupil 10 in Group 1: 72
Enter mark for pupil 1 in Group 2: 50
Enter mark for pupil 2 in Group 2: 62
Enter mark for pupil 3 in Group 2: 70
Enter mark for pupil 4 in Group 2: 77
Enter mark for pupil 5 in Group 2: 82
Enter mark for pupil 6 in Group 2: 91
Enter mark for pupil 7 in Group 2: 69
Enter mark for pupil 8 in Group 2: 74
Enter mark for pupil 9 in Group 2: 80
Enter mark for pupil 10 in Group 2: 68

Average mark for Group 1: 76.50
Average mark for Group 2: 73.30

Case 3:
Enter marks for 20 pupils (2 groups of 10):
Enter mark for pupil 1 in Group 1: 95
Enter mark for pupil 2 in Group 1: 97
Enter mark for pupil 3 in Group 1: 98
Enter mark for pupil 4 in Group 1: 94
Enter mark for pupil 5 in Group 1: 96
Enter mark for pupil 6 in Group 1: 92
Enter mark for pupil 7 in Group 1: 93
Enter mark for pupil 8 in Group 1: 98
Enter mark for pupil 9 in Group 1: 90
Enter mark for pupil 10 in Group 1: 91
Enter mark for pupil 1 in Group 2: 89
Enter mark for pupil 2 in Group 2: 91
Enter mark for pupil 3 in Group 2: 85
Enter mark for pupil 4 in Group 2: 87
Enter mark for pupil 5 in Group 2: 92
Enter mark for pupil 6 in Group 2: 90
Enter mark for pupil 7 in Group 2: 94
Enter mark for pupil 8 in Group 2: 88
Enter mark for pupil 9 in Group 2: 93
Enter mark for pupil 10 in Group 2: 95

Average mark for Group 1: 94.00
Average mark for Group 2: 90.60