Changing value in a array and display

Question

Hi I wrote a code that supposed display the name of each person and then able to select which ever person I pick, then it display they grade and let me able to change it. I got it to display they grade but I don't know how to change that persons grade value only, instead it changes every persons grade and displays it how do I change it? So it displays the change of that one person only? and add whatever value I want to it? And how do I display the changed value next to the persons name? If you could help me I be very thank full.

    static void Main(string[] args)
    {
        int selection;
        do
        {
            String[] A = { "Tim", "Jhon", "Sam", "Derp"};
            int[] B = { 90, 89, 60, 40 };
            DisplayMenu();
            Console.Write("Enter you selection: ");
            int.TryParse(Console.ReadLine(),out selection);
            switch (selection)
            {
                case 1:
                    Console.WriteLine(
            "{0}  ", B[0]);
                    AddToGrade(B);
                    break;
                case 2:
                    Console.WriteLine(
            "{0}  ", B[1]);
                    AddToGrade(B);
                    break;
                case 3:
                    Console.WriteLine(
            "{0}  ", B[2]);
                    AddToGrade(B);
                    break;
                default:
                    Console.WriteLine(
            "{0}  ", B[3]);
                    AddToGrade(B);
                    break;
            }
            Console.ReadKey();
        } while (selection != 4);

    }
    static void DisplayMenu()
    {
        Console.Clear();
        Console.WriteLine("Select a student 1-4");
        Console.WriteLine("1. Time");
        Console.WriteLine("2. Jhon");
        Console.WriteLine("3. Sam");
        Console.WriteLine("4. Derp");
    }
    static void AddToGrade(int[] array)
    {

        Console.WriteLine("Input New Value: ");
        int newValue = Convert.ToInt32(Console.ReadLine());
        for (int i = 0; i < array.Length; i++)
        {
            array[i] += newValue;
            Console.Write("New Grade: {0}", array[i]);
        }
    }

Answer 1

AddToGrade should accept index representing the grade to change.

static void AddToGrade(int[] array ,int index)
{
     Console.WriteLine("Input New Value: ");
     int newValue = Convert.ToInt32(Console.ReadLine());
     array[index] += newValue;
     Console.Write("New Grade: {0}", array[index]);
}

And after your switch (before the Console.ReadKey(); ) just call this:

AddToGrade(B, selection - 1);

Moreover, you should use more functions to make your code robust and elegant, eg (That example will also alliw you to keep the formatting in a single place)

static void DisplayNameGrade(int index, String[] A, int[] B)
{
    Console.WriteLine("Name: {0}, Grade: {1}", A[index], B[index])
}

Generally, you should learn the basic concepts of Object Oriented Programming , and design your code with classes, members and functions.