type of data:
| serial number | symbol | type | Space size (bytes) | initialization |
| 1 | char | character data type | 1 | char = 'a' ; or char = "abc"; |
| 2 | short | short integer | 2 | short a = 0; |
| 3 | int | plastic surgery | 4 | int a = 0; |
| 4 | long | long integer | 4 | long a =0; |
| 5 | long long | longer shaping | 8 | long long a = 0; |
| 6 | float | single precision floating point | 4 | float a = 12.1f ; |
| 7 | double | double precision floating point | 8 | double a = 12.12 |
Computer space unit conversion relationship:
The smallest unit: bit
| 1 byte (byte) | 8 bit |
| 1 KB | 1024 byte |
| 1MB | 1024 KB |
| 1GB | 1024 MB |
| 1TB | 1024 GB |
| 1PB | 1024 TB |
| ...... | ...... |
Variable Naming Rules
⭕ can only consist of letters (both uppercase and lowercase), numbers, and underscores ( _ ).
⭕ cannot start with a number.
⭕The length cannot exceed 63 characters.
⭕Case-sensitive in variable names.
⭕Variable names cannot use keywords.
escape character
Escape character (Escape character), all ASCII codes can be represented by "\" plus numbers (usually octal numbers). C defines some letters preceded by "\" to represent common ASCII characters that cannot be displayed, such as \0, \t, \n, etc., which are called escape characters, because the following characters are not original The ASCII characters mean it.
| escape character | paraphrase |
| \? | Used when writing multiple question marks in a row, preventing them from being parsed into three-letter words |
| \' | Used to represent character constants' |
| \" | Used to denote double quotes inside a string |
| \\ | Used to denote a backslash, preventing it from being interpreted as an escape sequence |
| \a | warning character, beep |
| \b | backspace |
| \f | Feed character |
| \n | new line |
| \r | carriage return |
| \t | horizontal tab |
| \v | vertical tab |
| \ddd | ddd represents 1~3 octal numbers. Such as: \130 X |
| \xdd | dd means 2 hexadecimal digits. Such as: \x30 0 |