if else

if age > 18 {
    print("成年人")
} else if age > 30 {
    print("中年人")
} else {
    print("小屁孩")
}

• if 后面只能是Bool类型
• if后面的条件可以省略小括号，条件后面的大括号不可以省略

white、repeat-while

• condition条件语句
• repeat-while相当于C语言的do-while

print("Hello, World!  While")
var num = 20
while num > 10 {
    print(num)
    num = num - 1;
}

print("Hello, World!  repeat While")
num = 20
repeat {
    print(num)
    num = num - 1;
} while num > 10