Swift控制语句

1、分支语句

        （1）条件语句if

                if

                else

                  if else

            (2)多分支语句switch

                switch语句可以使用整数，浮点数，字符，字符串和元组等类型，而且它的数值可以是离散的也可以是连续的范围，

                case分支不需要显式的添加break语句

                每个case后可以添加多个值，多个值之间用逗号分隔，每个switch必须有一个default语句，它放在所有分支后面，至少要有一个case语句

            (3)在switch中使用范围匹配

                      闭区间：....

                                 90...100 表示 90>=   =<100

                        半闭区间：..<   90..<100  表示 90<   <100

                        在case中使用下划线（_）忽略其中的字段值：

                                 var student=("id":"1002","name":"李四","age":"32","ChineseScore":80,"EnglishScore":90)

                                switch student{

                                            case (_,_,_,90...100,90...100):

                                                    descr="优"

                                              case(_,_,_,80...90,80...90):

                                                      descr="良"

                                                case(_,_,_,60...80,60...80):

                                                        descr="中"

                                                  case(_,_,_,60...80,90...100),(_,_,_,90...100,60...80):

                                                        descr="偏科"

                                                    case(_,_,_,0...60,90...100),(_,_,_,90...100,0...60):

                                                          descr="严重偏科"

                                                     default:

                                                            descr="无"

}

                        使用逗号分隔两个元组值，表示或关系

            （4）在Switch中比较元组的值绑定

                        使用元组的时候可以在case分支中将匹配的值绑定到一个临时的变量或常量，这些常量或变量能够在分支中使用，这成为值绑定

                                         var student=("id":"1002","name":"四","age":"32","ChineseScore":80,"EnglishScore":90)

                        switch student{

                            case (_,_,let age,90...100,90...100):

                                    if (age > 30){

                        descr="老人"

}

                                else{

                            descr="小孩"

}

}

            （5）在Switch中比较元组

                        在绑定元组值的时候，还可以在case中使用where语句，进行条件的过滤，类似于SQL语句中的where

                    switch student{

                                case (_,_,let age,90...100,90...100)where age >0:

                                                descr="优"

}

2、循环语句

        （1）while语句

                    while 循环条件{

                        语句组

}

        （2）do while语句

                do {

}while 条件

        （3）for语句

                    for 初始化;循环条件;迭代{

    }

        （4）for in语句

3、跳转语句

        （1）break语句

    break可以应用于switch语句和循环语句

                    label1: for var x=0;x<5;x++{

                            label2:for var y=5;y>0;y--{

                                            if (x==y){

                                            break label1

}

                                        println("(x.y)=(\(x),\(y))")

}

}

        （2）continue语句

        （3）fallthrough语句

                   贯通

                     让循环语句继续往下走

                        case 3:

                                i++

                                fallthrough

                           case 4:

                                 i++

                                fallthrough

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