iOS Development Swift-(four) operator

One, operator

Some of the operators supported by 1.Swift have the following

Assignment operator: =

Compound Assignment operators: + =,-=

Arithmetic operators: + 、-、 *,/

Remainder Operator:%

Self-increment, decrement operator: + + 、--

Comparison operators: = =,! =, >, <, >=, <=

Logical operators:&&, | |,!

Trinocular operator:? :

Range operators:.. < 、...

Overflow operators: &+, &-, &*, &/, &%

2. Assignment operators

(1) 1 to 1 assignment

var a = 5

Let B = 20

(2) N assignment to n (tuple)

Let (x, y) = (1, 2)//x is the value of 1,y is 2 and is constant

Note: Unlike C\oc, the assignment operator for Swift does not return a value

if (x = y) {}

The above code is wrong because x = y does not return a specific value

Description: This benefit is to prevent misuse = and = =

3. Arithmetic operators

Simple to use

1 + 2//3

5-3//2

2 * 3//6

10.0/2.5//4.0

"HTTP//" + "www.wendingding.cn"//"http://www.wendingding.cn"

4. Finding the remainder operator

% is called "redundancy operator" in Swift, and language is called "modulo operator".

9% 4//1

-9% 4//-1

9%-4//1

-9%-4//-1

Hint: the positive and negative of the remainder result is the same as the positive value of the left

Note: Unlike the C language, Swift's% supports calculation of floating-point numbers

8% 2.5//0.5

5.Bool type

The bool type, also known as the logical type (Logical), takes 2 values

True: True

False: False

Note: In the C language: 0 is false, not 0 is true, and there is no such concept in Swift

The condition of the IF statement must be a value of type bool

(1) Wrong wording

if (10) {

println ("conditions established")

}

(2) Correct wording

if (true) {

println ("conditions established")

}

6. Three mesh operator

The comparison operator \ Logical operator returns a value of type bool with a value of 2 possible

True: True, 6 > 5, (7 > 6) && (9! = 7)

False: False, 6 < 5, (7 >= 6) && (9 = = 7)

The condition of the trinocular operator must be a value of type bool

(1) Wrong wording

Let A = 10

Let C = a? 100:200

(2) Correct wording

Let c = a! = 0? 100:200

Let C = False? 100:200

7. Scope operators

The range operator is used to represent a range with 2 types of range operators

Closed range Operator: a...b, representing [A, b], containing A and b

Semi-closed range operator: A.. <b, which means [a, b], contains a, does not contain B

Example:

The value of index from

The value of index from 1~4

8. Overflow operator

(1) Brief description

Each data type has its own range of values, which, by default, generates a compile or run-time error once a value that exceeds the range of values is assigned

Note: The following notation is incorrect

Let x = Uint8.max

Let y = x + 1

The 2nd line of code will run the Times wrong (run-time error)

Tip: The above is a run-time error, and the following error is a compile-time error.

　　

Swfit provides 5 & start overflow operators for integer calculations that can be flexibly processed for values beyond the range of values

overflow addition &+

Overflow subtraction &-

Overflow multiplication &*

Overflow Division &/

Overflow to seek residual &%

(2) Overflow of values

Let x = Uint8.max

Let y = x &+ 1

After the 1th line of code: The value of x is 255 (maximum)

After the 2nd line of code: The value of y is 0 (minimum value)

(3) Underflow of the value

Let x = Uint8.min

Let y = x &-1

After the 1th line of code: The value of x is 0 (minimum value)

After the 2nd line of code: The value of Y is 255 (maximum)

　　

Signed integers also have similar overflow phenomena

Let x = Int8.min

Let y = x &-1

After the 1th line of code: The value of X is-128 (minimum value)

After the 2nd line of code: The value of Y is 127 (maximum)

　　

(4) Except 0 overflow

By default, a number is removed from 0, or the remainder is calculated for 0, and the compiler will directly error

Let x = 10

Let y = x/0

Let z = x% 0

2nd, 3 lines of code: the compiler will error

If you use the overflow operator, you will not get an error

Let x = 10

Let y = x &/0

Let z = x &% 0

The values of Y and Z are ultimately 0.

Second, assert

1. Brief description

Assertion is a method for real-time detection of whether the condition is true

If the condition is true, then the code continues to execute

If the condition is false, an error message is thrown to terminate the program's operation directly.

2. Usage of assertions

Using the global Assert function

The ASSERT function receives a BOOL expression and a message that appears when an assertion fails

ASSERT (Index >= 0, "Index must be greater than 0")

If index is greater than or equal to 0, continue with the following code

If index is less than 0, the error message (the black word below) is thrown, terminating the program's operation directly

Assertion Failed:index must be greater than 0

ASSERT (index >= 0)

Error messages can be omitted, but not recommended, which is not conducive to debugging

3. Usage scenarios and Notes

(1) The following scenario may be used to assert

Index of the instrumented array: cannot be too small or too large to cause the array to cross out

To detect arguments passed to a function: if it is an invalid parameter, it cannot be used in the function.

(2) Notice of use of assertions

Assertions can cause the program to abort, and if the condition is true, continue to execute code, you cannot use assertions

Assertions can ensure that errors are discovered in the development process, but it is best not to use them in published applications.

If a program suddenly crashes with the use of a utility, it can seriously affect the user experience

iOS Development Swift-(four) operator