public static TAccumulate AggregateRight<TSource, TAccumulate>(
  this IEnumerable<TSource> source, 
  TAccumulate acc, 
  Func<TAccumulate, TSource, TAccumulate> func)
{
  if (source == null)
    throw New ArgumentNullException("source");
  if (func == null)
    throw New ArgumentNullException("func");

  foreach (TSource item in source.Reverse())
    acc = func(seed, item);

  return acc;
}

for (int i = 0; i < array1.Length; i++)
{
  if (i != 0)
    result += ", ";

  result += array1[i];
}

var sb = new StringBuilder();
for (int i = 0; i < array1.Length; i++)
{
    if (i != 0)
    sb.Append(", ");
    sb.Append(array1[i]);
}
result = sb.ToString();