if_else.md

#控制结构：if-else if-else是我们熟知的一种控制结构。Lua 跟其他语言一样，提供了if-else的控制结构。因为是大家熟悉的语法，本节只简单介绍一下它的使用方法。

单个 if 分支 型

x = 10
if x > 0 then
    print("x is a positive number")
end

运行输出：x is a positive number

两个分支： if-else 型

x = 10
if x > 0 then
    print("x is a positive number")
else
    print("x is a non-positive number")
end

运行输出：x is a positive number

多个分支： if-elseif-else型

score = 90
if score == 100 then
    print("Very good!Your score is 100")
elseif score >= 60 then
    print("Congratulations, you have passed it,your score greater or equal to 60")
--此处可以添加多个elseif
else
    print("Sorry, you do not pass the exam! ")
end

运行输出：Congratulations, you have passed it,your score greater or equal to 60

与C语言的不同之处是elseif是连在一起的，若不else与if写成"else if"则相当于在else 里嵌套,如下代码：

score = 0
if score == 100 then
    print("Very good!Your score is 100")
elseif score >= 60 then
    print("Congratulations, you have passed it,your score greater or equal to 60")
else
    if score > 0 then  
        print("Your score is better than 0")
    else
        print("My God, your score turned out to be 0")
    end --与上一示例代码不同的是，此处要添加一个end
end

运行输出：My God, your score turned out to be 0