import std.stdio;
 
int main () { 
   /* local variable definition */
   int a=100; 

   /* check the boolean condition */
   if( a < 20 ) { 
      /* if condition is true then print the following */
      writefln("a is less than 20" ); 
   } else { 
      /* if condition is false then print the following */
      writefln("a is not less than 20" ); 
   } 
   writefln("value of a is : %d", a); 

   return 0; 
}

編譯并執(zhí)行上述代碼時，將生成以下結(jié)果-

a is not less than 20; 
value of a is : 100

if...elseif...else - 語句

If語句后面可以跟隨可選的Else If.Else語句，這對于使用單個If.Else If語句測試各種條件非常有用。

在使用If，Else語句時，有幾點需要牢記-

• if可以有零個或一個其他IF，并且它必須在任何其他IF之后。

• if可以有零到許多其他if，它們必須出現(xiàn)在else之前。

• 一旦Else If成功，就不會測試其余的Else If或Else。

D編程語言中if.else語句的語法是-

if(boolean_expression 1) { 
   /* Executes when the boolean expression 1 is true */
} else if( boolean_expression 2) { 
   /* Executes when the boolean expression 2 is true */
} else if( boolean_expression 3) { 
   /* Executes when the boolean expression 3 is true */
} else { 
   /* executes when the none of the above condition is true */
}

if...elseif...else - 示例

import std.stdio;
 
int main () { 
   /* local variable definition */
   int a=100; 

   /* check the boolean condition */
   if( a == 10 ) { 
      /* if condition is true then print the following */
      writefln("Value of a is 10" ); 
   } else if( a == 20 ) { 
      /* if else if condition is true */
      writefln("Value of a is 20" ); 
   } else if( a == 30 ) { 
      /* if else if condition is true  */
      writefln("Value of a is 30" ); 
   } else { 
      /* if none of the conditions is true */
      writefln("None of the values is matching" ); 
   } 
   writefln("Exact value of a is: %d", a ); 

   return 0; 
}

None of the values is matching 
Exact value of a is: 100