D语言嵌套的switch语句

import std.stdio;

int main () { 
   /* local variable definition */ 
   int a = 100; 
   int b = 200;  

   switch(a) {
      case 100: 
         writefln("This is part of outer switch", a ); 
         switch(b) { 
            case 200: 
               writefln("This is part of inner switch", a ); 
            default: 
               break; 
         } 
      default: 
      break; 
   } 
   writefln("Exact value of a is : %d", a ); 
   writefln("Exact value of b is : %d", b ); 

   return 0; 
}