#Julia Basic Syntax

# This is a single-line comment
x = 10  # End-of-line comment

#=
This is a multi-line comment
It can span multiple lines
For detailed explanations
=#

# Valid variable names
x = 1
my_variable = 2
变量 = 3        # Chinese supported
α = 0.5         # Greek letters supported
_private = 4

# Invalid variable names
# 2nd = 5       # Cannot start with digit
# for = 6       # Cannot use reserved word

# Single assignment
x = 10

# Multiple assignment
a, b, c = 1, 2, 3

# Swap variables
a, b = b, a

# Chained assignment
x = y = z = 0

const PI = 3.14159
const MAX_SIZE = 100

# Attempting to modify constants produces warnings
# PI = 3.14  # Warning: redefining constant

# Integers
a = 42          # Int64 (on 64-bit systems)
b = Int32(42)   # Int32

# Floating point
c = 3.14        # Float64
d = Float32(3.14)  # Float32

# Boolean
e = true
f = false

# Character (single quotes)
char = 'A'

# String (double quotes)
str = "Hello, Julia!"

# Multi-line string
multiline = """
This is a
multi-line string
"""

# print doesn't add newline
print("Hello")
print(" World")  # Output: Hello World

# println adds newline
println("Hello")
println("World")
# Output:
# Hello
# World

name = "Julia"
age = 10

println("$name is $age years old.")
# Output: Julia is 10 years old.

# Expression interpolation
println("2 + 3 = $(2 + 3)")
# Output: 2 + 3 = 5

using Printf

@printf("Integer: %d\n", 42)
@printf("Float: %.2f\n", 3.14159)
@printf("String: %s\n", "Hello")
@printf("Zero-padded: %05d\n", 42)  # Output: 00042

print("Enter your name: ")
name = readline()
println("Hello, $name!")

print("Enter a number: ")
input = readline()
num = parse(Int, input)
println("You entered: $num")

# Or use Float64
num_float = parse(Float64, readline())

# Suppress output
x = 10;

# Multiple statements on one line
a = 1; b = 2; c = 3

result = begin
    x = 10
    y = 20
    x + y  # Last expression value becomes block value
end
println(result)  # Output: 30

result = (x = 1; y = 2; x + y)
println(result)  # Output: 3

global_var = 100

function show_global()
    println(global_var)
end

function local_example()
    local_var = 10  # Local variable
    println(local_var)
end

# local_var not accessible outside function

let
    x = 10
    y = 20
    println(x + y)
end
# x and y not accessible outside let block

counter = 0

function increment()
    global counter
    counter += 1
end

increment()
println(counter)  # Output: 1

module MyModule

export greet  # Exported function

const VERSION = "1.0"

function greet(name)
    println("Hello, $name!")
end

function internal_function()
    # Internal function, not exported
end

end  # module

# Use all exported content from module
using MyModule
greet("Julia")

# Import only specific content
using MyModule: greet

# Import module itself
import MyModule
MyModule.greet("Julia")

using Statistics
using LinearAlgebra
using Random

# Using begin...end
z = begin
    x = 1
    y = 2
    x + y
end

# Using semicolon chain
z = (x = 1; y = 2; x + y)

x = 10
result = x > 5 ? "greater than 5" : "5 or less"
println(result)  # Output: greater than 5

# && - if first is true, execute second
x = 10
x > 5 && println("x is greater than 5")

# || - if first is false, execute second
x < 5 || println("x is not less than 5")

function no_return()
    println("This function returns nothing")
end

result = no_return()
println(result)        # Output: nothing
println(isnothing(result))  # Output: true

data = [1, 2, missing, 4, 5]

println(ismissing(data[3]))  # Output: true

# Missing propagation
println(1 + missing)  # Output: missing

# Skip missing values
using Statistics
println(mean(skipmissing(data)))  # Output: 3.0

# Variable type annotation
x::Int = 10

# Function parameter types
function add(a::Int, b::Int)
    return a + b
end

# Return type
function multiply(a, b)::Float64
    return a * b
end