📅 最后修改于: 2020-11-03 15:53:16 🧑 作者: Mango
运算符是一个符号，告诉编译器执行特定的数学或逻辑操作。 Objective-C语言包含丰富的内置运算符，并提供以下类型的运算符-
本教程将逐一说明算术，关系，逻辑，按位，赋值和其他运算符。
下表显示了Objective-C语言支持的所有算术运算运算符。假设变量A持有10，变量B持有20，则-
| Operator | Description | Example |
|---|---|---|
| + | 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 |
下表显示了Objective-C语言支持的所有关系运算符。假设变量A持有10，变量B持有20，则-
| Operator | Description | Example |
|---|---|---|
| == | 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. |
下表显示了Objective-C语言支持的所有逻辑运算符。假设变量A保持1，变量B保持0，则-
| Operator | Description | Example |
|---|---|---|
| && | 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. |
按位运算符对位进行运算并执行逐位操作。 ＆，|和^的真值表如下-
| 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A = 60;和B = 13;现在以二进制格式，它们将如下所示-
A = 0011 1100
B = 0000 1101
—————–
A＆B = 0000 1100
A | B = 0011 1101
A ^ B = 0011 0001
〜A = 1100 0011
下表列出了Objective-C语言支持的按位运算符。假设变量A保持60，变量B保持13，然后-
| Operator | Description | Example |
|---|---|---|
| & | 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 |
Objective-C语言支持以下赋值运算符-
| Operator | Description | Example |
|---|---|---|
| = | 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 |
还有其他几个重要的运算符，包括sizeof和? ：受Objective-C语言支持。
| Operator | Description | Example |
|---|---|---|
| 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 |
运算符优先级确定表达式中术语的分组。这会影响表达式的求值方式。某些运算符具有更高的优先级；例如，乘法运算符的优先级比加法运算符-
例如，x = 7 + 3 * 2;在这里，x被赋值为13，而不是20，因为运算符*的优先级比+高，因此它首先与3 * 2相乘，然后加到7。
在此，优先级最高的运算符出现在表格的顶部，优先级最低的运算符出现在表格的底部。在表达式中，优先级较高的运算符将首先被评估。
| Category | Operator | Associativity |
|---|---|---|
| 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 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 |