Strings in Lua

-- Single quotes
local str1 = 'Hello World'

-- Double quotes
local str2 = "Hello World"

-- Square brackets (for multi-line strings)
local str3 = [[
This is a multi-line string
that can span multiple lines
without any escape characters.
]]

print(str1)
print(str2)
print(str3)

local first = "Hello"
local last = "World"
local greeting = first .. " " .. last
print(greeting)  -- Hello World

-- Numbers are converted to strings when concatenated
local age = 25
local message = "I am " .. age .. " years old"
print(message)  -- I am 25 years old

-- Multiple concatenations
local text = "a" .. "b" .. "c" .. "d"
print(text)  -- abcd

local text = "Hello Lua"
print(#text)  -- 9

local empty = ""
print(#empty)  -- 0

local multiline = [[
Line 1
Line 2
Line 3
]]
print(#multiline)  -- 21 (includes newlines)

local text = "Hello\nWorld"      -- Newline
local quote = "He said \"Hi!\""  -- Double quote
local tab = "First\tSecond"       -- Tab
local backslash = "C:\\Users\\John"  -- Backslash

print(text)
print(quote)
print(tab)
print(backslash)

local text = "Hello, World!"

-- Convert to uppercase
local upper = string.upper(text)
print(upper)  -- HELLO, WORLD!

-- Convert to lowercase
local lower = string.lower(text)
print(lower)  -- hello, world!

-- Reverse string
local reversed = string.reverse(text)
print(reversed)  -- !dlroW ,olleH

-- Get substring
local sub = string.sub(text, 1, 5)  -- From position 1 to 5
print(sub)  -- Hello

-- Find substring
local pos = string.find(text, "World")
print(pos)  -- 8 (starting position)

-- Replace substring
local replaced = string.gsub(text, "World", "Lua")
print(replaced)  -- Hello, Lua!

-- Format strings (similar to C's printf)
local name = "Alice"
local age = 30
local height = 5.6

local formatted = string.format("Name: %s, Age: %d, Height: %.1f", name, age, height)
print(formatted)  -- Name: Alice, Age: 30, Height: 5.6

-- Number formatting
local pi = 3.14159
print(string.format("%.2f", pi))        -- 3.14
print(string.format("%08d", 42))       -- 00000042
print(string.format("%x", 255))         -- ff (hexadecimal)
print(string.format("%o", 8))           -- 10 (octal)

local text = "The price is $42.50"

-- %d matches any digit
local price = string.match(text, "%d+%.%d+")
print(price)  -- 42.50

-- %a matches any letter
local letters = string.match("abc123", "%a+")
print(letters)  -- abc

-- %s matches whitespace
local words = string.match("hello world", "%S+")
print(words)  -- hello

-- . matches any character
local match = string.match("abc", ".")
print(match)  -- a

local text = "Call me at 555-123-4567"

-- + matches one or more
local digits = string.match(text, "%d+")
print(digits)  -- 555

-- * matches zero or more
local pattern = string.match("abc", ".*")
print(pattern)  -- abc

-- ? matches zero or one
local optional = string.match("color", "colou?r")
print(optional)  -- color

local text = "[email protected]"

-- [a-z] matches any lowercase letter
local lowercase = string.match(text, "[a-z]+")
print(lowercase)  -- ser

-- [A-Z] matches any uppercase letter
local uppercase = string.match(text, "[A-Z]")
print(uppercase)  -- U

-- [0-9] matches any digit (same as %d)
local number = string.match(text, "[0-9]+")
print(number)  -- 123

-- ^ at start of character class negates it
local non_digits = string.match(text, "[^0-9]+")
print(non_digits)  -- User

local text = "hello"

for i = 1, #text do
    local char = string.sub(text, i, i)
    print(i, char)
end

-- Alternative using gmatch
for char in string.gmatch(text, ".") do
    print(char)
end

function split_string(str, delimiter)
    local result = {}
    for match in (str .. delimiter):gmatch("(.-)" .. delimiter) do
        table.insert(result, match)
    end
    return result
end

local text = "apple,banana,orange,grape"
local fruits = split_string(text, ",")

for i, fruit in ipairs(fruits) do
    print(i, fruit)
end

local function is_valid_email(email)
    -- Basic email validation
    local pattern = "^[%w._%+-]+@[%w.-]+%.%a%a%a?$"
    return string.match(email, pattern) ~= nil
end

print(is_valid_email("[email protected]"))     -- true
print(is_valid_email("invalid.email"))         -- false
print(is_valid_email("user@domain"))           -- false

local function count_words(text)
    local count = 0
    for word in string.gmatch(text, "%S+") do
        count = count + 1
    end
    return count
end

local sentence = "The quick brown fox jumps over the lazy dog"
print("Word count:", count_words(sentence))  -- 9

local function clean_whitespace(text)
    -- Remove leading and trailing whitespace
    local cleaned = string.match(text, "^%s*(.-)%s*$")
    
    -- Replace multiple spaces with single space
    cleaned = string.gsub(cleaned, "%s+", " ")
    
    return cleaned
end

local messy = "   Hello   there   world!   "
local clean = clean_whitespace(messy)
print("'" .. clean .. "'")  -- 'Hello there world!'

local function get_url_param(url, param_name)
    local pattern = param_name .. "=([^&]*)"
    return string.match(url, pattern)
end

local url = "https://example.com?name=John&age=30&city=NewYork"
print(get_url_param(url, "name"))  -- John
print(get_url_param(url, "age"))   -- 30
print(get_url_param(url, "city"))  -- NewYork

-- Efficient string building
local parts = {}
for i = 1, 1000 do
    parts[i] = "Part " .. i
end
local result = table.concat(parts, ", ")