# D語言if...else語句

## 語法

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

D編程語言假設任何非零和非空值作爲true，如果是零或null，則假定爲false。

## 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語句

• if可以有零個或else，它必須跟在else if後面。

• if 可以有零到多個else if，它們必須在else之前。

• 一旦一個 else if 匹配成功，剩餘else if不會被測試或計算。

## 語法

if...else if...else語句在D編程語言的語法是：

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 */ }

## 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