字符串 #

s1 = "Hello, Julia!"
s2 = "你好，世界！"
s3 = ""

s = """
这是一个
多行字符串
"""

s = raw"C:\Users\name\file.txt"

typeof("Hello")
typeof("你好")

c1 = 'A'
c2 = '中'
c3 = '\u2200'

typeof('A')

'A' == "A"
'A' === "A"
string('A')
first("Hello")

Int('A')
Int('中')
Char(65)
Char(20013)
codepoint('A')

isdigit('5')
isalpha('A')
isalnum('A')
islower('a')
isupper('A')
isspace(' ')
ispunct('!')

s = "Hello"
s[1]
s[5]
s[begin]
s[end]

s = "你好"
s[1]
length(s)
sizeof(s)

s = "你好"
i = firstindex(s)
while i <= lastindex(s)
    println(s[i])
    global i = nextind(s, i)
end

s = "你好世界"
for i in eachindex(s)
    println(i, " => ", s[i])
end

s = "Hello, Julia!"
s[1:5]
s[8:end]
s[begin:5]
s[1:2:end]

s = "Hello, Julia!"
sub = s[1:5]
typeof(sub)
String(sub)

s = "Hello, Julia!"
sub = @view s[1:5]

"Hello" * ", " * "Julia"

string("Hello", ", ", "Julia")
string(1, 2, 3)

join(["Hello", "Julia"], ", ")
join([1, 2, 3], "-")

"Julia" ^ 3
repeat("Julia", 3)

split("Hello,Julia,World", ",")
split("Hello Julia World")
split("a,b;c:d", [',', ';', ':'])

replace("Hello, World!", "World" => "Julia")
replace("Hello, World!", "o" => "0")
replace("Hello, World!", 'o' => '0', count=1)

strip("  Hello  ")
lstrip("  Hello  ")
rstrip("  Hello  ")
strip("\n\tHello\n\t")

uppercase("hello")
lowercase("HELLO")
titlecase("hello world")
uppercasefirst("hello")
lowercasefirst("HELLO")

s = "Hello, Julia!"
findfirst("Julia", s)
findfirst("l", s)
findlast("l", s)
findnext("l", s, 4)
findprev("l", s, 10)

s = "Hello, Julia!"
occursin("Julia", s)
occursin("World", s)
startswith(s, "Hello")
endswith(s, "!")
contains(s, "Julia")

s = "Hello, Julia!"
count('l', s)
count("l", s)

name = "Julia"
println("Hello, $name!")

x = 10
y = 20
println("$x + $y = $(x + y)")

arr = [1, 2, 3]
println("Array: $arr, Sum: $(sum(arr))")

println("Dollar sign: \$")
println("Backslash: \\")

using Printf

@printf("Integer: %d\n", 42)
@printf("Float: %.2f\n", 3.14159)
@printf("String: %s\n", "Julia")
@printf("Width: %10d\n", 42)
@printf("Left: %-10d|\n", 42)

using Printf
s = @sprintf("%.2f", 3.14159)

using Format

fmt"{} + {} = {}"(1, 2, 3)
fmt"{:.2f}"(3.14159)

re = r"hello"
typeof(re)

re = r"\d+"
occursin(re, "abc123def")
m = match(re, "abc123def")
m.match
m.offset

re = r"\d+"
eachmatch(re, "abc123def456ghi789")
collect(eachmatch(re, "abc123def456ghi789"))

re = r"\d+"
replace("abc123def456", re => "NUM")
replace("abc123def456", re => s"NUM")

re = r"(\d+)-(\d+)"
m = match(re, "abc123-456def")
m[1]
m[2]
m.captures

re = r"hello"i
occursin(re, "HELLO")

re = r"hello."s
match(re, "hello\nworld")

"hello" == "hello"
"hello" == "Hello"
"hello" === "hello"

"abc" < "abd"
"abc" < "abcd"
"abc" < "ABC"

lowercase("Hello") == lowercase("hello")
casecmp("Hello", "hello")

parse(Int, "42")
parse(Float64, "3.14")
parse(Int, "FF", base=16)
tryparse(Int, "42")
tryparse(Int, "abc")

string(42)
string(3.14)
string(255, base=16)
string(255, base=2, pad=8)

function word_count(text::String)
    words = split(lowercase(text))
    counts = Dict{String, Int}()
    for word in words
        w = strip(word, ['.', ',', '!', '?', ';', ':'])
        counts[w] = get(counts, w, 0) + 1
    end
    return counts
end

text = "Hello, world! Hello, Julia!"
word_count(text)

function is_palindrome(s::String)
    cleaned = lowercase(replace(s, r"\W" => ""))
    return cleaned == reverse(cleaned)
end

is_palindrome("A man, a plan, a canal: Panama")
is_palindrome("Hello")

function format_table(headers::Vector{String}, rows::Vector{Vector{String}})
    widths = [maximum(length.(col)) for col in zip(headers, eachrow(hcat(rows...))...)]
    
    function format_row(row, widths)
        join([lpad(cell, w) for (cell, w) in zip(row, widths)], " | ")
    end
    
    println(format_row(headers, widths))
    println(join(["-"^w for w in widths], "-+-"))
    for row in rows
        println(format_row(row, widths))
    end
end

headers = ["Name", "Age", "City"]
rows = [["Alice", "25", "New York"], ["Bob", "30", "Los Angeles"]]
format_table(headers, rows)

function extract_emails(text::String)
    re = r"[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}"
    [m.match for m in eachmatch(re, text)]
end

text = "Contact us at info@example.com or support@test.org"
extract_emails(text)