Swift控制语句

分支语句

 

1. 条件语句 if-else ，基本语法形式如下，其中 “[]” 中 的部分可以省略。

 

 

if boolean-expression {

statement1;


}  [else if boolean-expression    {

statement2;

}  ] [else  {
statement3;


}  ]

 

实例：

 

 

var number1 = 0;

var number2 = 1;

var max = 0;

if number1 >number2 {

max = number1;

} else if number1 < number2 {

max = number2;

} else {

max = number1;

}
println("Themaximum is \(max)")

 

 

2 ．多分支语句 switch 它的语法形式如下：

 

 

switch some value to consider {

case value 1:

respond to value 1 case value 2,                value 3:
respond to value 2 or 3

default:

otherwise, do something else

}

 

 

 

每个 case 不需要显式地添加 break ，每个 case 至少有 一条语句。

 

可以比较任何类型。

实例１：

 

 

let someCharacter: Character ="e" switch someCharacter {
case "a", "e", "i","o", "u":

println("\(someCharacter) isa vowel")case "b", "c", "d", "f", "g", "h", "j", "k", "l","m", "n", "p", "q", "r", "s", "t", "v", "w", "x", "y", "z":
println("\(someCharacter) is a consonant")

default:

println("\(someCharacter)  is not  a  vowel   or  a consonant")

}

 

 

实例２：

 

 

let count = 3_000

let countedThings = "stars inthe Milky Way"varnaturalCount: String
switch count {

case 0:

naturalCount ="no" case 1...3:
naturalCount ="a few" case 4...9:
naturalCount ="several"

case 10...99:

naturalCount ="tens of" case 100...999:
naturalCount ="hundreds of" case 1000...999_999:
naturalCount ="thousands of"

default:

naturalCount = "millions and millions of"


}

println("There are \(naturalCount) \(countedThings).")

 

 

 

 

循环语句

 

while语句

 

do-while语句

 

for语句

 

for in语句

while 循环

 

while condition{

statements

}
vari = 100 varr = 0 vars= 0 vart = 0
while i < 1000 {

r= i / 100

s=( i - r* 100 ) / 10

t= i - r* 100 - s* 10

if( i == r * r* r + s* s *s + t* t * t){

println ( "i = \(i)" )

}
i++
}
do while 循环
do {

statements

} while condition
vari = 100 varr = 0 vars= 0 vart = 0

do      {

r= i / 100

s=( i - r* 100 ) / 10

t= i - r* 100 - s* 10

if( i == r * r* r + s* s *s + t* t * t){
 println ("i = \(i)" )

}
i++
} while i < 1000

 

 

for 循环

 

for initialization; condition; increment {
statements
}
vari= 8 varr = 0 vars= 0
forvarj =0; j <=i; j++{

r = j * j

s=j * j * j

println (" 整数为 :\(j) ");

println (" 对应的平方和 :\( r)")

println ( " 对应的立方和 : \( s ) " )

}

 

 

for in 循环

 

用于遍历集合。

 

1.  遍历范围

 

forindex in1...5{

println( " \(index) times 5 is \(index * 5 )" )

}

 

 

2.  忽略循环变量

 

 

letbase = 3

letpower = 10 varanswer = 1
for_ in 1...power {

answer *=base

}

println (" \(base )to the power of \(power )is \(answer ) " )

 

 

 

 

3.  遍历数组

 

 

letnames =[ "Anna" ,"Alex" , "Brian" ,"Jack"]

forname innames {

println( "Hello, \(name) !" )

}

 

4.  遍历字典

 

 letnumberOfLegs =[ "spider" :8 , "ant" :6 , "cat" : 4]

for(animalName, legCount) innumberOfLegs {

println( " \(animalName) s have \(legCount) legs" )

}

 

 

5 .遍历字符串

 

 

 

 letnumberOfLegs =[ "spider" :8 , "ant" :6 , "cat" : 4]

for(animalName, legCount) innumberOfLegs {

println( " \(animalName) s have \(legCount) legs" )

}
 letnumberOfLegs =[ "spider" :8 , "ant" :6 , "cat" : 4]

for(animalName, legCount) innumberOfLegs {

println( " \(animalName) s have \(legCount) legs" )

}

 

 

1.12.3 跳转语句

 

 •   continue

 •   break

 

•   fallthrough

 

•   return

 

 

 

 

 

1.continue 实例：

 

 

for var i = 0; i < 100; i++ {

if i % 10 == 0 {

continue;

}

println("i = \(i)");

}

 

2. break 实例：

 

 

for var i = 0; i < 10;i++ {

if i == 3 {
 break;
 }
println("i = \(i)");
}
 println("Game Over!");

 

3. fallthrough 实例：

 

 

let integerToDescribe = 5
 var description = "Thenumber \(integerToDescribe) is"
 switchintegerToDescribe {
 case 2, 3, 5, 7, 11, 13, 17, 19:
 description += " a prime number, and also"fallthrough
default:
 description += " an integer."
}

println(description)

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