Swift Learning (II.)

2. Control Flow:

There are three main types of statements

• If,switch and the new guard

• For,while

• Break,continue

About IF

The conditions in the statement no longer require the use of () packages.

1234	let number = 23ifnumber < 10 {    print("The number is small")}

However, the code behind the judgment execution must be wrapped with {}.

The condition after the if must be a Boolean expression

That is, it is not implicitly compared to 0, which is wrong, because number is not a Boolean expression, number! = 0 is.

123	int number = 0ifnumber{}

About for

The For loop becomes more convenient and more powerful in Swift.

Benefit from Swift's newly added range operator ... and ...<

We are able to use the tedious for loop:

1234	for(int i = 1; i <= 5; i++){    NSLog(@"%d", i);}

Overwrite to:

123	forindex in1...5 {    print(index)}

Although no similar usage is mentioned in the Swift programming Language, we have an elegant approach in swift.

123	forindex instride(from: 1, through: 5, by: 2) {    print(index)}// through是包括5

Then the traversal of the dictionary is enhanced. In the fast enumeration of objective-c we can only enumerate the keys of the dictionary.

1234	NSString *key;for(key insomeDictionary){     NSLog(@"Key: %@, Value %@", key, [someDictionary objectForKey: key]);}

In Swift, through tuple we can enumerate both key and value:

1234	let dictionary = ["firstName":"Mango","lastName":"Fang"]for(key,value) indictionary{    print(key+" "+value)}

About switch:

Swich also gained enhanced functionality and increased security in swift.

No break is required to terminate the next case execution

That is, the following two types of notation are equivalent.

123456789

let character = "a"switchcharacter{    case"a":        print("A")    break    case"b":        print("B")    breakdefault: print("character")

1234567

let character = "a"switchcharacter{    case"a":        print("A")    case"b":        print("B")default: print("character")

This improvement avoids forgetting to write the error caused by the break, I have a deep experience, it was because of the omission of the write-off and spent a period of time to debug.

If we want to treat different values uniformly, separate the values with commas.

1234	switchsome value to consider {casevalue 1,value 2:    statements}

In Swift, the type of switch support has been greatly broadened.

This means that in development we are able to match strings, floating-point numbers, and so on.

Previously, the tedious wording of OC could be improved:

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if([cardName isEqualToString:@"Six"]) {    [self setValue:6];} elseif([cardName isEqualToString:@"Seven"]) {    [self setValue:7];} elseif([cardName isEqualToString:@"Eight"]) {    [self setValue:8];} elseif([cardName isEqualToString:@"Nine"]) {    [self setValue:9];}

12345678910

switchcarName{    case"Six":        self.vaule = 6    case"Seven":        self.vaule = 7    case"Eight":        self.vaule = 8    case"Night":        self.vaule = 9   }

Swift Learning (II.)