它始終是合法的，在D編程嵌套if-else語句，這意味著你可以使用一個if或else if語句在另一個if或else if語句。

語法

嵌套的if語句的語法如下：

if( boolean_expression 1)
{
   /* Executes when the boolean expression 1 is true */
   if(boolean_expression 2)
   {
      /* Executes when the boolean expression 2 is true */
   }
}

可以嵌套else if...else 以類似的方式，如嵌套的if語句。

例子：

import std.stdio;
 
int main ()
{
   /* local variable definition */
   int a = 100;
   int b = 200;
 
   /* check the boolean condition */
   if( a == 100 )
   {
       /* if condition is true then check the following */
       if( b == 200 )
       {
          /* if condition is true then print the following */
          writefln("Value of a is 100 and b is 200" );
       }
   }
   writefln("Exact value of a is : %d", a );
   writefln("Exact value of b is : %d", b );
 
   return 0;
}

當上麵的代碼被編譯並執行，它會產生以下結果：

Value of a is 100 and b is 200
Exact value of a is : 100
Exact value of b is : 200