📅 最后修改于: 2020-11-03 16:13:44 🧑 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。 Pascal允许以下类型的运算符-
让我们一一讨论算术，关系，布尔和位运算符。稍后我们将讨论集合运算符和字符串运算。
下表显示了Pascal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 |
下表显示了Pascal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Pascal语言支持的所有布尔运算符。所有这些运算符都对布尔操作数起作用，并产生布尔结果。假设变量A为真，变量B为假，则-
| Operator | Description | Example |
|---|---|---|
| and | Called Boolean AND operator. If both the operands are true, then condition becomes true. | (A and B) is false. |
| and then | It is similar to the AND operator, however, it guarantees the order in which the compiler evaluates the logical expression. Left to right and the right operands are evaluated only when necessary. | (A and then B) is false. |
| or | Called Boolean OR Operator. If any of the two operands is true, then condition becomes true. | (A or B) is true. |
| or else | It is similar to Boolean OR, however, it guarantees the order in which the compiler evaluates the logical expression. Left to right and the right operands are evaluated only when necessary. | (A or else B) is true. |
| not | Called Boolean NOT Operator. Used to reverse the logical state of its operand. If a condition is true, then Logical NOT operator will make it false. | not (A and B) is true. |
按位运算符对位进行运算并执行逐位操作。所有这些运算符都对整数操作数起作用，并产生整数结果。按位和(＆)，按位或(|)和按位非(〜)的真值表如下-
| p | q | p & q | p | q | ~p | ~q |
|---|---|---|---|---|---|
| 0 | 0 | 0 | 0 | 1 | 1 |
| 0 | 1 | 0 | 1 | 1 | 0 |
| 1 | 1 | 1 | 1 | 0 | 0 |
| 1 | 0 | 0 | 1 | 0 | 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 0001
〜A = 1100 0011
下表列出了Pascal支持的按位运算符。假设变量A保持60，变量B保持13，则：
| 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 OR Operator copies a bit if it exists in either operand. Its same as | operator. | (A ! B) will give 61, which is 0011 1101 |
| ~ | 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 due to a signed binary number. |
| << | 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 |
请注意，Pascal的不同实现在按位运算运算符有所不同。 Free Pascal，我们在这里使用的编译器，但是支持以下按位运算运算符-
| Operators | Operations |
|---|---|
| not | Bitwise NOT |
| and | Bitwise AND |
| or | Bitwise OR |
| xor | Bitwise exclusive OR |
| shl | Bitwise shift left |
| shr | Bitwise shift right |
| << | Bitwise shift left |
| >> | Bitwise shift right |
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高于加法运算符。
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。
| Operator | Precedence |
|---|---|
| ~, not, | Highest |
| *, /, div, mod, and, & | |
| |, !, +, -, or, | |
| =, <>, <, <=, >, >=, in | |
| or else, and then | Lowest |