C语言：

memset
   extern void *memset(void *buffer,int c,int count);
   #include <string.h>
   功能：把buffer所指内存区域的前count个字节设置成字符c
   说明：返回指向buffer的指针.

char a[100];
          memset(a,‘\0‘,sizeof(a));

C#:

byte[]   test =   new   byte[65536];    

Array.Clear(test,0,test.Length);  

You could use Enumerable.Repeat:

byte[] a = Enumerable.Repeat((byte)10, 100).ToArray();

The first parameter is the element you want repeated, and the second parameter is the number of times to repeat it.

This is OK for small arrays but you should use the looping method if you are dealing with very large arrays and performance is a concern.

(C/C++) memset