lua 语句学习

就如同C里的if else,while,do,repeat。就看lua里怎么用：

1、首先看if else

t = {1,2,3}

local i = 1

if t[i] and t[i] % 2 == 0 then
print("even")
else
print("odd")
end

lua木有C里的&&，而是and来表示；if 之后跟表达式，之后要更个then 最后语句结束都要写end 表示这个chunk结束了。

2、while

while t[i] do
print(t[i])
i = i + 1
end

3、do end

do
print(t[i])
i = i + 1
end

4、repeat until

local i = 1
repeat
print(t[i])
i = i + 1
until t[i] == nil

5、for的使用方法

for i = 1, #t do
print(t[i])
end

当然for循环里还能够直接调用lua API

for k,v in pairs(t) do
print(k , v)
end

6、break使用方法

for k,v in pairs(t) do
print(k , v)
if k == 2 then
break
end
end

课后题解答：

1、lua为毛支持elseif这样的写法

比方能够这么写：

for k,v in pairs(t) do
if k == 2 then
print('111')
elseif k == 1 then
print(k , v)
end
end

这样整个if ...end是一个chunk；假设if else分开写，就得这样：

t = {1,2,3}


for k,v in pairs(t) do
if k == 2 then
print('111')
else if k == 1 then
print(k , v)
end
end
end

多出了一个end。

由于lua里没有switch，假设选择分支比較多写那么多end非常丑陋，so就能够elseif一起用啦。

2、写无条件运行代码，假设c里我喜欢用do{}while(false)；lua就能够有非常多写法，来个最easy想到的：

local i = 0
repeat
i = i + 1
print(i)
if i > 10 then
break
end
until false

3、第三个问题，我已经用第二个解答回答了，在lua里是要用到repeat until来做的。

4、改动恶心的goto语句，的确看着非常不爽。改了就清爽多了：

function room1()
repeat
local move = io.read()
if move == "south" then
return room3()
elseif move == "east" then
return room2()
else
print("invalid move")
end
until false
end

function room2()
repeat
local move = io.read()
if move == "south" then
return room4()
elseif move == "west" then
return room1()
else
print("invalid move")
end
until false
end

function room3()
repeat
local move = io.read()
if move == "north" then
return room1()
elseif move == "east" then
return room4()
else
print("invalid move")
end
until false
end

function room4()
print("Congratulations, u win!")
end

room1()

5、goto的限制

goto不能调到某个语句块内。由于内部是不能为外部所知道的。为毛不能跳出函数块，书里的解释是：

stackflow的答案是：

Your guesses are hinting at the answer. The reason is because the ​​goto​​ statement and its destination must reside in the same stack frame. The program context before and after the ​ ​goto​​ need to be the same otherwise the code being jumped to won't be running in its correct stack frame and its behavior will be undefined. ​ ​goto​​ in C has the same restrictions for the same reasons.

6、这道题看到goto就好凌乱，我压根就打算用goto。也驾驭不了介个，so不分析了。