swift流程控制_03_swift基本使用

//: Playground - noun: a place where people can play

import UIKit


//1.if语句实现条件选择
//（1）单分支
var age = 9

if age < 10 {
    
    print("年龄小于10岁")
}

//(2)双分支 
var oranges = 20
var apples = 30

if oranges < apples {
    
    print("苹果多")
} else {
    
    print("桔子多")
}


//(3)多分支
var score = 65
var grade : Character;

if score >= 90 {
    grade = "A"
} else if score >= 80 {
    
    grade = "B"
} else if score >= 70 {
    
    grade = "C"
} else if score >= 60 {
    
    grade = "D"
} else {
    grade = "F"
}

print("grade=(grade)")


//2. switch语句实现条件选择
/*
(1)switch后面的表达式可以整型，浮点型，字符，字符串，数值可以是单个的，也可以是一段范围
(2)case分支不需要加break语句，分支执行完毕以后会自动的跳出switch
(3)必须有default，必须放在所有分支的最后面
(4)每个case必须有至少一条语句,如果想匹配多个条件，可以用一个case将多个条件用逗号隔开

*/
var light = "Green"

switch light {
    
case "Red":
    print("停")
case "Yellow","Green":
    print("注意小心通过")
default:
    print("灯坏了")
    
}

switch score {
case 90...100: //[90,100]
    grade = "A"
case 80..<90: //[80,90)
    grade = "B"
case 70..<80:
    grade = "C"
case 60..<70:
    grade = "D"
default:
    grade = "F"
    
}

//3.while和do while
var j = 10;

repeat {
    print(j)
    j--
    

} while j > 0

//4. for循环
//当循环体中的操作与循环变量无关时，循环变量可以用_代替
for _ in 0...10 {
    print("next")
    
}

//5.控制转移语句
//(1)break和continue
for  k in 0..<10 {
    if k == 3 {
        continue;
    }
    
    print(k)
}

//(2)fallthrough:用于switch语句中多个条件的混合处理
let intergerToDescribe = 5

var description = "The number (intergerToDescribe) is"

switch intergerToDescribe {
case 2,3,5,7,11,13,17,19:
    description += " a prime number, and also"
    fallthrough
default:
    description += " an integer"
    
    
}

print(description)

//(3)标签:用于复杂的循环处理，用标签来进行标识流程控制
label1:for var x = 0; x < 5; x++ {
    for var y = 5; y > 0; y-- {
        
        if y == x {
            break label1;
        }
        
        print("(x,y)=((x),(y))")
        
    }
    
    
    
    
}