# if 語句:

if語句由一個布爾表達式後跟一個或多個語句。

## 語法:

if語句的語法是：

if expression then
-- Statements will execute if the expression is true
end if

if 布爾表達式的值爲true，那麼裏面的代碼塊，if語句會被執行。如果不是第一組結束後的代碼，if 語句將被執行。

## 示例:

#!/home/euphoria-4.0b2/bin/eui

integer a = 10
integer b = 20

if (a + b) < 40 then
printf(1, "%s\n", {"This is true if statement!"})
end if

if (a + b) > 40 then
printf(1, "%s\n", {"This is not true if statement!"})
end if

This is true if statement!

# if...else 語句:

if語句後面可以通過一個可選的else語句，布爾表達式爲 false 時執行。

## 語句:

if...else 語句的語法是:

if expression then
-- Statements will execute if the expression is true
else
-- Statements will execute if the expression is false
end if

## 示例:

#!/home/euphoria-4.0b2/bin/eui

integer a = 10
integer b = 20

if (a + b) < 40 then
printf(1, "%s\n", {"This is inside if statement!"})
else
printf(1, "%s\n", {"This is inside else statement!"})
end if

This is inside if statement!

# if...elsif...else 語句:

if語句後面可以跟任意數量的可選elsif...else語句，這是非常有用的，以測試各種條件下使用單個if...elsif語句。

## 語法:

if...elsif...else 語法是:

if expression1 then
-- Executes when the Boolean expression 1 is true
elsif expression2 then
-- Executes when the Boolean expression 2 is true
elsif expression3 then
-- Executes when the Boolean expression 3 is true
else
-- Executes when none of the above condition is true.
end if

## 示例:

#!/home/euphoria-4.0b2/bin/eui

integer a = 10
integer b = 20

if (a + b) = 40 then
printf(1, "Value of (a + b ) is %d\n", a + b )
elsif (a + b) = 45 then
printf(1, "Value of (a + b ) is %d\n", a + b )
elsif (a + b) = 30 then
printf(1, "Value of (a + b ) is %d\n", a + b )
else
printf(1, "Value of (a + b ) is %d\n", 0 )
end if

Value of (a + b ) is 30

# if...label...then 語句:

if 語句可以有一個標籤子句之前 then 關鍵字。需要注意的是elsif  子句不能有一個label。

if label塊和標籤名稱必須用雙引號的字符串常量，有單個或多個字。label關鍵字是區分大小寫的，應該寫成label。 .

## 語法:

label 子句語法：

if expression label "Label Name" then
-- Executes when the boolean expression is true
end if

## 例子:

#!/home/euphoria-4.0b2/bin/eui

integer a = 10
integer b = 20

if (a + b) = 40 label "First IF Block" then
printf(1, "Value of (a + b ) is %d\n", a + b )
elsif (a + b) = 45 then
printf(1, "Value of (a + b ) is %d\n", a + b )
elsif (a + b) = 30 then
printf(1, "Value of (a + b ) is %d\n", a + b )
else
printf(1, "Value of (a + b ) is %d\n", 0 )
end if

Value of (a + b ) is 30

# 嵌套 if...else 語句:

## 語法:

if expression1 then
-- Executes when the boolean expression1 is true
if expression2 then
-- Executes when the boolean expression2 is true
end if
end if

## 例子:

#!/home/euphoria-4.0b2/bin/eui

integer a = 10
integer b = 20
integer c = 0

if c = 0 then
printf(1, "Value of c is equal to %d\n", 0 )
if (a + b) = 30 then
printf(1, "Value of (a + b ) is equal to %d\n", 30)
else
printf(1, "Value of (a + b ) is equal to %d\n", a + b )
end if
else
printf(1, "Value of c is equal to %d\n", c )
end if

Value of c is equal to 0
Value of (a + b ) is equal to 30