There are three basic logical operations:

1) The logical AND- is represented by AB: when both A and B are 1, its value is 1, otherwise it is zero.

2) The logical OR- is represented by A+B: when both A and B are 0, their values are 0; otherwise, it is 1.

3) Logical negation-use "?" About A. It means that when A=0, the negation of A is 1, and when A= 1, the negation of A is 0.

Functions of logical expressions:

A meaningful formula that connects relational expressions or logical quantities with logical operators is called a logical expression, and the value of a logical expression is a logical value, that is, "true" or "false".

C language compiler system uses the number 1 to indicate "true" and the number 0 to indicate "false" when giving the logical operation result, but when judging whether a quantity is "true", it uses 0 to indicate "false" and non-zero to indicate "true", and can assign the operation result of logical expression (0 or 1) to integer variables or character variables.