设一数组a[6]={2,7,6,8,10,21}, 请设计一递归函数，并在main函数中调用该函数求所给数组的和。（要求求和函数务必是递归结构）

#include <stdio.h>

int sum(int a[],int n)
{
    if(n<=0)
        return 0;
    else
        return a[0] + sum(a+1,n-1);
}

int main()
{
    int a[6]={2,7,6,8,10,21};
    int s = sum(a,6);
    printf("%d",s);
    return 0;
}

    static void Main(string[] args)
    {
        Console.WriteLine("Hello World!");
        int[] a = new int[6]{ 2, 7, 6, 8, 10, 21 };
        var sum=Sum(a, a.Length-1);
        int Sum(int[] list,int vernier)
        {
            if (vernier < 0) return 0;
            return list[vernier]+Sum(list, --vernier);
        }
        Console.WriteLine($"求和结果为{sum}");
        Console.ReadLine();
    }