Swift控制語句

1、分支語句

        （1）條件語句if

                if

                else

                  if else

            (2)多分支語句switch

                switch語句可以使用整數，浮點數，字符，字符串和元組等類型，而且它的數值可以是離散的也可以是連續的范圍，

                case分支不需要顯式的添加break語句

                每個case后可以添加多個值，多個值之間用逗號分隔，每個switch必須有一個default語句，它放在所有分支后面，至少要有一個case語句

            (3)在switch中使用范圍匹配

                      閉區間：....

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

                        半閉區間：..<   90..<100  表示 90<   <100

                        在case中使用下劃線（_）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="優"

                                              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="嚴重偏科"

                                                     default:

                                                            descr="無"

}

                        使用逗號分隔兩個元組值，表示或關系

            （4）在Switch中比較元組的值綁定

                        使用元組的時候可以在case分支中將匹配的值綁定到一個臨時的變量或常量，這些常量或變量能夠在分支中使用，這成為值綁定

                                         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中比較元組

                        在綁定元組值的時候，還可以在case中使用where語句，進行條件的過濾，類似于SQL語句中的where

                    switch student{

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

                                                descr="優"

}

2、循環語句

        （1）while語句

                    while 循環條件{

                        語句組

}

        （2）do while語句

                do {

}while 條件

        （3）for語句

                    for 初始化;循環條件;迭代{

    }

        （4）for in語句

3、跳轉語句

        （1）break語句

    break可以應用于switch語句和循環語句

                    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語句

        （3）fallthrough語句

                   貫通

                     讓循環語句繼續往下走

                        case 3:

                                i++

                                fallthrough

                           case 4:

                                 i++

                                fallthrough