条件语句 #

if condition
    statements
end

x = 10

if x > 0
    println("x is positive")
end

x = -5

if x > 0
    println("x is positive")
else
    println("x is not positive")
end

x = 0

if x > 0
    println("x is positive")
elseif x < 0
    println("x is negative")
else
    println("x is zero")
end

score = 85

if score >= 90
    println("A")
elseif score >= 80
    println("B")
elseif score >= 70
    println("C")
elseif score >= 60
    println("D")
else
    println("F")
end

x = 10
result = if x > 0
    "positive"
else
    "non-positive"
end
println(result)

x = 10
result = if x > 0
    y = x * 2
    y + 1
else
    0
end

condition ? value_if_true : value_if_false

x = 5
result = x > 0 ? "positive" : "non-positive"

x = 0
result = x > 0 ? "positive" : x < 0 ? "negative" : "zero"

x = 5

result = x > 0 ? "positive" : "non-positive"

result = if x > 0
    "positive"
else
    "non-positive"
end

x = 5
x > 0 && println("x is positive")

x < 0 && println("This won't print")

x = 5
x < 0 || println("x is non-negative")

x > 0 || println("This won't print")

function safe_divide(a, b)
    b == 0 && return nothing
    return a / b
end

function get_default(dict, key, default)
    haskey(dict, key) && return dict[key]
    return default
end

x, y = 5, 3

if x > 0
    if y > 0
        println("Both positive")
    else
        println("x positive, y not")
    end
else
    println("x not positive")
end

x, y = 5, 3

if x > 0 && y > 0
    println("Both positive")
elseif x > 0
    println("x positive, y not")
else
    println("x not positive")
end

x = 10

if x isa Int
    println("Integer: $x")
elseif x isa Float64
    println("Float: $x")
elseif x isa String
    println("String: $x")
end

function process(x)
    if x isa Int
        x * 2
    elseif x isa Float64
        x / 2
    elseif x isa String
        uppercase(x)
    else
        x
    end
end

function grade(score)
    if score >= 90
        "A"
    elseif score >= 80
        "B"
    elseif score >= 70
        "C"
    elseif score >= 60
        "D"
    else
        "F"
    end
end

grade(85)
grade(72)
grade(55)

function is_leap_year(year)
    (year % 4 == 0 && year % 100 != 0) || year % 400 == 0
end

is_leap_year(2000)
is_leap_year(1900)
is_leap_year(2024)

function classify_number(n)
    if n == 0
        "Zero"
    elseif n > 0
        if n % 2 == 0
            "Positive Even"
        else
            "Positive Odd"
        end
    else
        if n % 2 == 0
            "Negative Even"
        else
            "Negative Odd"
        end
    end
end

classify_number(10)
classify_number(-5)
classify_number(0)

function calculator(a, op, b)
    if op == "+"
        a + b
    elseif op == "-"
        a - b
    elseif op == "*"
        a * b
    elseif op == "/"
        b == 0 ? error("Division by zero") : a / b
    else
        error("Unknown operator: $op")
    end
end

calculator(10, "+", 5)
calculator(10, "/", 2)