loadrunner中itoa函数报错memory violation : Exception ACCESS_VIOLATION received.

变量类型报错
Action()
{
  char filename[20];
   char Cstring;    --------》   修改为 char Cstring[10];就不报错了
   int Cint=100;
   if (itoa((Cint,Cstring,10))
   lr_output_message("ok");
  sprintf (filename, "log_%s.txt",Cstring); 
  lr_output_message ("New file name %s", filename); 

   return 0;

}

报错：
Virtual User Script started at : 2016-01-26 14:30:49
Starting action vuser_init.
Web Turbo Replay of LoadRunner 11.0.0 for Windows 7; build 8859 (Aug 18 2010 20:14:31)   [MsgId: MMSG-27143]
Run Mode: HTML   [MsgId: MMSG-26000]
Run-Time Settings file: "D:\loadrunner11\scriptCTest\\default.cfg"   [MsgId: MMSG-27141]
Ending action vuser_init.
Running Vuser...
Starting iteration 1.
Starting action Action.
Action.c(18): Error: C interpreter run time error: Action.c (18):  Error -- memory violation : Exception ACCESS_VIOLATION received.
Action.c(18): Notify: CCI trace: Action.c(18): itoa(100, 0, 10)
.
Action.c(18): Notify: CCI trace: Compiled_code(0): Action()
.
Ending Vuser...
Starting action vuser_end.
Ending action vuser_end.
Vuser Terminated.