发布于 2015-07-05 11:57:13 | 270 次阅读 | 评论: 0 | 来源: 网络整理
运算符是一个符号，它告诉编译器执行特定的数学或逻辑操作。 Objective-C语言有丰富的内置运算符并提供了以下几种类型：
算术运算符
关系运算符
逻辑运算符
位运算符
赋值运算符
其他运算符
本教程将逐个讲解算术表达式，关系逻辑，按位分配和其他运算符。
下表列出了所有支持Objective-C语言的算术运算符。假设变量A=10，变量B=20，则：
| 运算符 | 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语言的关系运算符。假设变量A=10和变量B=20，则：
| 运算符 | 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语言的逻辑运算符。假设变量A=1，变量B=0，那么：
| 运算符 | 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. |
位运算符位和位操作执行位。 &, |, 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 |
假设，如果A=60和B=13; 现在以二进制格式将如下：
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语言的位运算符。假设变量A=60和变量B=13，那么：
| 运算符 | 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语言的赋值运算符有以下：
| 运算符 | 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 |
一些其他重要的运算符，包括sizeof 和 ? :支持Objective-C语言。
| 运算符 | 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. |
| * | Pointer to a variable. | *a; will pointer to a variable. |
| ? : | Conditional Expression | If Condition is true ? Then value X : Otherwise value Y |
运算符优先级确定在表达式中的分组。这会影响如何计算一个表达式。某些运算符有比别人更高的优先级，例如，乘法运算符的优先级高于加法运算符：
例如，X=7+3* 2;这里，x是分配13，不是20，因为运算符*的优先级高于+，所以它首先被乘以3 * 2，然后加7。
在这里，运算符具有最高优先级，出现在上面的表中，那些与最低的出现在底部。在一个表达式中，优先级较高的运算符将首先计算。
| 类别 | 运算符 | 关联性 |
|---|---|---|
| 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 |