Objective-C 運算符

運算符是一個符號，它告訴編譯器執行特定的數學或邏輯操作。 Objective-C語言有豐富的內置運算符並提供了以下幾種類型：

• 算術運算符

• 關係運算符

• 邏輯運算符

• 位運算符

• 賦值運算符

• 其他運算符

本教程將逐個講解算術表達式，關係邏輯，按位分配和其他運算符。

算術運算符

下表列出了所有支持Objective-C語言的算術運算符。假設變量A=10，變量B=20，則：

顯示實例

運算符

描述

示例

+

Adds two operands

A + B will give 30

-

Subtracts second operand from the first

A - B will give -10

*

Multiplies both operands

A * B will give 200

/

Divides numerator by denominator

B / A will give 2

%

Modulus Operator and remainder of after an integer division

B % A will give 0

++

Increment operator increases integer value by one

A++ will give 11

--

Decrement operator decreases integer value by one

A-- will give 9

關係運算符

下表列出了所有支持Objective-C語言的關係運算符。假設變量A=10和變量B=20，則：

顯示實例

運算符

描述

示例

==

Checks if the values of two operands are equal or not; if yes, then condition becomes true.

(A == B) is not true.

!=

Checks if the values of two operands are equal or not; if values are not equal, then condition becomes true.

(A != B) is true.

>

Checks if the value of left operand is greater than the value of right operand; if yes, then condition becomes true.

(A > B) is not true.

<

Checks if the value of left operand is less than the value of right operand; if yes, then condition becomes true.

(A < B) is true.

>=

Checks if the value of left operand is greater than or equal to the value of right operand; if yes, then condition becomes true.

(A >= B) is not true.

<=

Checks if the value of left operand is less than or equal to the value of right operand; if yes, then condition becomes true.

(A <= B) is true.

邏輯運算符

下表列出了所有支持Objective-C語言的邏輯運算符。假設變量A=1，變量B=0，那麼：

顯示實例

運算符

描述

示例

&&

Called Logical AND operator. If both the operands are non zero then condition becomes true.

(A && B) is false.

||

Called Logical OR Operator. If any of the two operands is non zero then condition becomes true.

(A || B) is true.

!

Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true, then Logical NOT operator will make false.

!(A && B) is true.

位運算符

位運算符位和位操作執行位。 &, |, 和 ^ 真值表如下：

p

q

p & q

p | q

p ^ q

0

0

0

0

0

0

1

0

1

1

1

1

1

1

0

1

0

0

1

1

假設，如果A=60和B=13; 現在以二進制格式將如下：

A = 0011 1100

B = 0000 1101

-----------------

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A  = 1100 0011

下表中列出了支持Objective-C語言的位運算符。假設變量A=60和變量B=13，那麼：

顯示實例

運算符

描述

例子

&

Binary AND Operator copies a bit to the result if it exists in both operands.

(A & B) will give 12, which is 0000 1100

|

Binary OR Operator copies a bit if it exists in either operand.

(A | B) will give 61, which is 0011 1101

^

Binary XOR Operator copies the bit if it is set in one operand but not both.

(A ^ B) will give 49, which is 0011 0001

~

Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.

(~A ) will give -61, which is 1100 0011 in 2's complement form.

<<

Binary Left Shift Operator. The left operands value is moved left by the number of bits specified by the right operand.

A << 2 will give 240, which is 1111 0000

>>

Binary Right Shift Operator. The left operands value is moved right by the number of bits specified by the right operand.

A >> 2 will give 15, which is 0000 1111

賦值運算符

支持Objective-C語言的賦值運算符有以下：

顯示例子

運算符

描述

示例

=

Simple assignment operator, Assigns values from right side operands to left side operand

C = A + B will assign value of A + B into C

+=

Add AND assignment operator, It adds right operand to the left operand and assigns the result to left operand

C += A is equivalent to C = C + A

-=

Subtract AND assignment operator, It subtracts right operand from the left operand and assigns the result to left operand

C -= A is equivalent to C = C - A

*=

Multiply AND assignment operator, It multiplies right operand with the left operand and assigns the result to left operand

C *= A is equivalent to C = C * A

/=

Divide AND assignment operator, It divides left operand with the right operand and assigns the result to left operand

C /= A is equivalent to C = C / A

%=

Modulus AND assignment operator, It takes modulus using two operands and assigns the result to left operand

C %= A is equivalent to C = C % A

<<=

Left shift AND assignment operator

C <<= 2 is same as C = C << 2

>>=

Right shift AND assignment operator

C >>= 2 is same as C = C >> 2

&=

Bitwise AND assignment operator

C &= 2 is same as C = C & 2

^=

bitwise exclusive OR and assignment operator

C ^= 2 is same as C = C ^ 2

|=

bitwise inclusive OR and assignment operator

C |= 2 is same as C = C | 2

其他運算符 ↦ sizeof & 三元

一些其他重要的運算符，包括sizeof 和 ? :支持Objective-C語言。

顯示示例

運算符

描述

例子

sizeof()

Returns the size of an variable.

sizeof(a), where a is integer, will return 4.

&

Returns the address of an variable.

&a; will give actual address of the variable.

*

Yiibaier to a variable.

*a; will yiibaier to a variable.

? :

Conditional Expression

If Condition is true ? Then value X : Otherwise value Y

Objective-C中的運算符優先級

運算符優先級確定在表達式中的分組。這會影響如何計算一個表達式。某些運算符有比別人更高的優先級，例如，乘法運算符的優先級高於加法運算符：

例如，X=7+3* 2;這裏，x是分配13，不是20，因爲運算符*的優先級高於+，所以它首先被乘以3 * 2，然後加7。

在這裏，運算符具有最高優先級，出現在上面的表中，那些與最低的出現在底部。在一個表達式中，優先級較高的運算符將首先計算。

類別

運算符

關聯性

Postfix 

() [] -> . ++ - -  

Left to right 

Unary 

+ - ! ~ ++ - - (type)* & sizeof 

Right to left 

Multiplicative  

* / % 

Left to right 

Additive  

+ - 

Left to right 

Shift  

<< >> 

Left to right 

Relational  

< <= > >= 

Left to right 

Equality  

== != 

Left to right 

Bitwise AND 

& 

Left to right 

Bitwise XOR 

^ 

Left to right 

Bitwise OR 

| 

Left to right 

Logical AND 

&& 

Left to right 

Logical OR 

|| 

Left to right 

Conditional 

?: 

Right to left 

Assignment 

= += -= *= /= %=>>= <<= &= ^= |= 

Right to left 

Comma 

, 

Left to right