math.randomseed(os.time())

math.random(10000)-----------------------1~10000

math.random ([m [, n]])

This function is an interface to the simple pseudo-random generator function rand provided by ANSI C. (No guarantees can be given for its statistical properties.)

When called without arguments, returns a uniform pseudo-random real number in the range [0,1). When called with an integer number m, math.random returns a uniform pseudo-random integer in the range [1, m]. When called with two integer numbers m and n, math.random returns a uniform pseudo-random integer in the range [m, n]. 

The Table Library

for name, line in pairsByKeys(lines) do
      print(name, line)
end

function pairsByKeys (t, f)
      local a = {}
      for n in pairs(t) do table.insert(a, n) end-------------t陣列的鍵複製到a陣列
      

      table.sort(a, f)
      

local i = 0      -- iterator variable
      local iter = function ()   -- iterator function
         i = i + 1
         if a[i] == nil then return nil
         else return a[i], t[a[i]]----------------------------------a陣列的值a[i],t陣列的值t[a[i]]

         end
      end
      return iter
 end

String Library

string.find(來源字串,目標字串) 回傳找到的開頭位置,結束位置，找不到回傳Nil

string.sub(來源字串,開頭位置，結束位置) 回傳指定區間的字串

s = "hello world"
i, j = string.find(s, "hello")
print(i, j)                      --> 1    5
print(string.sub(s, i, j))       --> hello
print(string.find(s, "world"))   --> 7    11
i, j = string.find(s, "l")
print(i, j)                      --> 3    3
print(string.find(s, "lll"))     --> nil

string.gsub(來源字串，欲取代的來源字串，欲取代的目標字串) 

回傳1取代完的目標字串

回傳2取代次數

string.gfind改成gmatch(s, pattern)

s = "hello world from Lua"
     for w in string.gmatch(s, "%a+") do
       print(w)
     end

輸出：

hello
world
from
Lua

s = string.gsub("Lua is cute", "cute", "great")
print(s)         --> Lua is great
s = string.gsub("all lii", "l", "x")
print(s)         --> axx xii
s = string.gsub("Lua is great", "perl", "tcl")
print(s)         --> Lua is great

'[0-9]' is simpler when written as '%d'

'[0-9a-fA-F]' is the same as '%x'---------------------------->16進位

'[^0-7]' finds any character that is not an octal digit

'%S' is simpler than '[^%s]'.

To count the number of vowels in a text, you can write

_, nvow = string.gsub(text, "[AEIOUaeiou]", "")----------->回傳字母數

print(string.gsub("one, and two; and three", "%a+", "word"))
--> word, word word; word word(一個以上的字母串)

i, j = string.find("the number 1298 is even", "%d+")
    print(i,j)   --> 12  15 (string.find會回傳開頭位置，結束位置)(%d+ --> 一個以上的數字串)

test = "int x; /* x */  int y; /* y */"
    print(string.gsub(test, "/%*.*%*/", "<COMMENT>"))
      --> int x; <COMMENT>

1.這段函示碼的目的是把註解變成<COMMENT>

2.%*這樣寫無效化*的作用

3." . "點這個字元代表任何字元，" .* "就變成0個以上的任何字串(可有可無)

4." / "不向反斜線字元，沒有任何作用。

5. int y; /* y */ 這字串被吃掉了，因為點*的關係，讓<COMMENT>取代的目標是 "/* x */  int y; /* y */"

test = "int x; /* x */  int y; /* y */"
    print(string.gsub(test, "/%*.-%*/", "<COMMENT>"))
        --> int x; <COMMENT>  int y; <COMMENT>

將".*"換成".-"的話，就可以"點到為止了"

 '[+-]?%d+' matching numerals like "-12", "23" and "+1009"

[+-]本來是+或- 多個問號變成有第三個選擇 "無"

if string.find(s, "^%d") then ...

checks whether the string s starts with a digit

抓數字開頭的字串(^的作用，注意不要跟[^0-7]這種互斥用法搞混)

if string.find(s, "^[+-]?%d+$") then ...

checks whether that string represents an integer number, without other leading or trailing characters.

抓整數值的字串，$錢字號在這裡的作用就是以數字結尾，所以不會有小數點連在一起。

Another item in a pattern is the '%b', that matches balanced strings. Such item is written as '%bxy', where x and y are any two distinct characters; the x acts as an opening character and the y as the closing one. For instance, the pattern '%b()' matches parts of the string that start with a `(´ and finish at the respective `)´:

    print(string.gsub("a (enclosed (in) parentheses) line",
                      "%b()", ""))
      --> a  line(目的是把括弧內的字串刪掉)

Typically, this pattern is used as '%b()', '%b[]', '%b%{%}', or '%b<>', but you can use any characters as delimiters.

"%bxy"，這裡的x和y是相對應的東西，有左括弧必有右括弧之類的。

The I/O Library

> print("hello", "Lua"); print("Hi")
      --> hello   Lua
      --> Hi
    
> io.write("hello", "Lua"); io.write("Hi", "\n")
      --> helloLuaHi

io.write不加料