PHP Reading Notes (4)-Operator

What is an operator

　What is an operator? Operators are identifiers that tell PHP to perform related operations. For example, if you need to calculate the value of 123 times 456, you need a symbol to tell the server that you need to do multiplication.

What are the operators in PHP? PHP operators are generally divided into arithmetic operators, assignment operators, comparison operators, ternary operators, logical operators, string concatenation operators, and error control operators.

Arithmetic operators in PHP

Arithmetic operators are mainly used for arithmetic operations, such as addition, subtraction, multiplication, and division. The commonly used arithmetic operators in PHP correspond to the following table:

Assignment operator in PHP

　 There are two assignment operators in PHP, namely:

(1) "=": Assign the value of the expression on the right to the operand on the left. It copies the value of the expression on the right and gives it to the operand on the left. In other words, a memory is allocated for the operand on the left first, and then the copied value is placed in this memory.

(2) "&": reference assignment, which means that both variables point to the same data. It will cause two variables to share a piece of memory. If the data stored in this memory changes, the values ​​of both variables will change.

Comparison operators in PHP

　Comparison operators are mainly used for comparison operations, such as: equal, congruent, not equal, greater than, less than. The commonly used comparison operators in PHP are as follows:

　

Ternary operator in PHP

　 ("?:") The ternary operator is also a comparison operator. For the expression (expr1)?(expr2):(expr3), if the value of expr1 is true, then the value of this expression is expr2, otherwise expr3.

("?:") The ternary operator is also a comparison operator. For the expression (expr1)?(expr2):(expr3), if the value of expr1 is true, then the value of this expression is expr2, otherwise expr3.

Logical operators in PHP

　Logical operators are mainly used to perform logical operations, such as logical AND, logical OR, logical XOR, logical NOT, etc. The commonly used logical operators in PHP are as follows:

　We can understand logical operations from the perspective of voting:

1. Logical AND: Requires everyone to vote to agree before an agreement can be passed;

2. Logical OR: Only one person is required to vote for approval;

3. Logical XOR: Only one and only one person can vote to agree;

4. Logical negation: Someone wants to object, but the objection is invalidated through logical negation;

The reason why "AND" and "OR" have two different forms of operators is the priority of their operations (that is, the limited order of operations. For example, when we were in elementary school, we learned the four arithmetic operations, and addition, subtraction, multiplication and division were mixed together. La, it is different to calculate multiplication and division first, then addition and subtraction).

We can understand logical operations from the perspective of voting:

1. Logical AND: Requires everyone to vote to agree before an agreement can be passed;

2. Logical OR: Only one person is required to vote for approval;

3. Logical XOR: Only one and only one person can vote to agree;

4. Logical negation: Someone wants to object, but the objection is invalidated through logical negation;

String concatenation operator in PHP

　The string concatenation operator is used to concatenate two strings. The string concatenation operators provided in PHP are:

(1) Concatenation operator ("."): It returns the string obtained by appending the right parameter to the left parameter.

(2) Connection assignment operator (“.="): It appends the right parameter to the left parameter.

Error control operators in PHP

　PHP provides an error control operator "@". For some expressions that may go wrong during operation, we do not want to display error messages to customers when errors occur, which is not user-friendly. . Therefore, @ can be placed before a PHP expression, and any error messages that may be generated by the expression will be ignored;

If the track_error feature (this thing is set in php.ini) is activated, any error information generated by the expression is stored in the variable $php_errormsg. This variable will be overwritten every time an error occurs. So you must check it out as early as possible if you want to use it.

It should be noted that the error control prefix "@" will not block parsing error information. It cannot be placed before the definition of a function or class, nor can it be used in conditional structures such as if and foreach.

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The reason why "AND" and "OR" have two different forms of operators is the priority of their operations (that is, the limited order of operations. For example, when we were in elementary school, we learned the four arithmetic operations, and addition, subtraction, multiplication and division were mixed together. La, it is different to calculate multiplication and division first, then addition and subtraction).