add cpp mark to code style

docs/cpp/functions-with-variable-argument-lists-cpp.md

@@ -31,7 +31,7 @@ Function declarations in which the last member of  is the ellipsis (...) can tak
 
  The following example shows how the macros work together with the type (declared in \<stdarg.h>): 
 
-```  
+```cpp  
 // variable_argument_lists.cpp  
 #include <stdio.h>  
 #include <stdarg.h>  
@@ -113,4 +113,4 @@ void ShowVar( char *szTypes, ... ) {
 
 3.  You should explicitly cast the result obtained by using the `va_arg` macro to the type that you want.  
 
- You must call the  macro to terminate variable-argument processing.`va_end`
+ You must call the  macro to terminate variable-argument processing.`va_end`