D语言if...else语句

一个if语句后面可以跟一个可选的else语句，该语句执行时的布尔表达式为false。

语法

在D编程语言的if... else语句的语法是：

if(boolean_expression)
{
   /* statement(s) will execute if the boolean expression is true */
}
else
{
  /* statement(s) will execute if the boolean expression is false */
}

如果布尔表达式的值为true，那么if代码块将被执行代码，否则else块将被执行。

D编程语言假设任何非零和非空值作为true，如果是零或null，则假定为false。

流程图：

例子：

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;
}

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

if...else if...else语句

一个if后面可以跟一个可选的if... else语句，如果测试各种条件下... else if语句，可使用单一的else语句。

当使用 if , else if , else语句有几点要记住：

• if可以有零个或else，它必须跟在else if后面。

• if 可以有零到多个else if，它们必须在else之前。

• 一旦一个 else if 匹配成功，剩余else if不会被测试或计算。

语法

if...else if...else语句在D编程语言的语法是：

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 */
}

例子：

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