How to count occurences of an int in an array?

Question

My array is A = {2, 3, 4, 3, 4, 2, 4, 2, 4}

I need an array B that stock at the index i the number of occurences of i in the a

Answer 1

This seems to be a homework or a tutorial. You have good solutions in Linq, but here is a simple version with basic algorithm:

static void Main(string[] args)
{
    int [] A = new int[4];
    // you should determine the size of B dynamically here...
    // Try to find yourself!
    int [] B = new int[999];

    /*  Code forgotten : initialize array B to 0s */

    for (int i = 0; i < A.Length; i++)
    {
        int item = A[i];
        // increase the number at index item
        B[item]++;
    }

}