Try:
int[] data = new int[] {2,8,18,32,50,72,98,128,168,200};
int total = 0;
for (int index = 0; index < data.Length; index++)
{
total += data[index];
}
Console.WriteLine(total);
But a better way:
int[] data = new int[] {2,8,18,32,50,72,98,128,168,200};
Console.WriteLine(data.Sum(x => x));