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：

本教學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：

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

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：

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.

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：

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; 現在以二進製格式將如下：

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：

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

支持Objective-C語言的賦值運算符有以下：

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

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

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

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。某些運算符有比彆人更高的優先級，例如，乘法運算符的優先級高於加法運算符：

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

在這裡，運算符具有最高優先級，出現在上麵的表中，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。