Constant in programming C

Constant refers to fixed values ​​that the program cannot change during execution. Those fixed values ​​are also called literals .

Constants can be any data type as data types: integers, real numbers, characters or strings . There are enumeration constants (enumeration).

A constant can be thought of as a variable often in addition to its value cannot be changed after being defined.

Integer constant in C

The integer constant value can be decimal (decimal), octal (octal) or hexadecimal (hexadecimal). The prefix (basic prefix) defines the base or radix: 0x or 0X for hexadecimal (system 16), 0 for octal (system 8), and nothing is decimal.

A constant value may have a suffix (combination) of U and L, for Unsigned and Long types . The ending may be uppercase or lowercase in any order.

Here is an example for the type of integer constant:

 212 /* la hop le */ 215u /* la hop le */ 0xFeeL /* la hop le */ 078 /* Khong hop le: 8 khong la ky so trong he bat phan (octal) */ 032UU /* Khong hop le: ban khong the lap lai hau to (suffix) */ 

Here are other examples with a few ways to declare with integer types:

 85 /* he thap phan */ 0213 /* he bat phan (octal) */ 0x4b /* he thap luc phan (hexadecimal) */ 30 /* int */ 30u /* unsigned int */ 30l /* long */ 30ul /* unsigned long */ 

Real constant in C

A floating point real constant has an integer part, a decimal value, a fractional part, and a exponent. You can represent floating point values ​​in decimal and fractional types.

When representing values ​​in decimal format, you must add integers, exponents, or both. The hat is written by e or E.

Here are a few examples for floating point sections:

 3.14159 /* Hop le */ 314159E-5L /* Hop le */ 510E /* Khong hop le: phan mu chua hoan thien */ 210f /* Khong hop le: khong co phan decimal va phan mu */ . e55 /* Khong hop le: thieu phan phan so va phan nguyen */ 

Hang characters in C

The character part is closed and closed in single quotes ('), for example' x 'and can be stored in a simple variable of type char .

A character can be a lowercase letter (eg 'x') or escape string (eg, 't'), or a universal character (eg 'u02C0').

There are specific characters in C when starting with a sign will have special meaning and are used to represent new lines (n), new tabs (t). Here is a list of special characters:

Escape sequence Meaning Character 'Character' "Character"? Characters ? a Bell b Backspace f Form feed n New line r Carriage return tab horizontal v tab vertical ooo Number in base 8 of 1 to 3 digits xhh. . . Hexadecimal number of one or more digits

Here is an example to show some escape sequence characters:

 #include int main () { printf ( "HoctLaptTrinhtCtTaitQTMnn" ); printf ( "===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); return 0 ; } 

Compile and run the above C program to see the results

Hang string in C

The string constant is enclosed with "" quotes. A string consists of characters similar to a character constant: pure characters, escape sequences and common characters .

You can divide long lines into lines using string values ​​and separate them by spaces.

Here are a few examples with string constants. The following three strings have the same value:

 "hello, vietnam" "hello, vietnam" "hello, " "v" "ietnam" 

Constant definition in C

There are two simple ways in C to define constants:

1. Use #define preprocessor .
2. Using const keyword.

Use the #define preprocessor in C

Below is a sample to use the #define preprocessor to define a constant:

 #define dinh_danh gia_tri 

Here is a detailed example:

 #include #define CHIEUDAI 15 #define CHIEURONG 12 #define NEWLINE 'n' int main () { int dientich ; dientich = CHIEUDAI * CHIEURONG ; printf ( "Dien tich hinh chu nhat la: %d" , dientich ); printf ( "%c" , NEWLINE ); printf ( "===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); return 0 ; } 

Compile and run the above C program to see the results

Use the const keyword in C

You can use the const prefix to declare constants with a specific type as follows:

 const kieu_du_lieu ten_bien = gia_tri ; 

Here is a detailed example:

 #include int main () { const int CHIEUDAI = 15 ; const int CHIEURONG = 12 ; const char NEWLINE = 'n' ; int dientich ; dientich = CHIEUDAI * CHIEURONG ; printf ( "Dien tich hinh chu nhat la: %d" , dientich ); printf ( "%c" , NEWLINE ); printf ( "===========================n" ); printf ( "QTM chuc cac ban hoc tot! n" ); return 0 ; } 

Compiling and running the above C program will produce the same results as above.

Note that in practice, we often name the word " CA" .

According to Tutorialspoint

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