Description
C Constants are same as the identifiers which are fixed values and cannot be modified once they are defined. Constants are represented by a name in the program. This name can be used same as the variable name.
C Constants of type integer can be declared in the following two ways.
1) Defining C Constants with const keyword : This keyword is a modifier that can be applied to any variable declaration. A variable declared to be const cant be modified during program execution. It is only initialised only at the time of declaration.
Const int a=1;
Int const a=1;
2) Defining C constants with #define directive : Directive #define is also used to declare the constants.
#define a 1 (pre-processor directive)
- When #define is used, all constants gets replaced with their actual values before compilation by the pre-processor and const is used by the compiler.
- #define is always global, const can be local(global also).
- #define does not have type checking where as type checking is part of const.
Types
| Constant | Meaning |
|---|---|
| Integer Constant | Constant which stores integer value |
| Floating Constant | Constant which stores float value |
| Character Constant | Constant which stores character value |
| String Constant | Constant which stores string value |
Description
An Integer constant may be decimal (base 10), octal (base 8), or hexadecimal (base 16) number which represents an integral value.
- Integer constant can be preceded by a sign either + or –.
- They can suffixed with U or L or sometimes both. U represents "Unsigned integer constant" and L represents "Long integer constant". UL represents "Unsigned Long Integer Constant."
- Spaces,non-digit characters and commas are not allowed in integer constants.
Description
Decimal integer constants takes values from 0 to 9. Sign is optional.
- Octal integer constant: Octal integer constants takes values form 0 to 7. The value is preceded by 0. For example, 0123.
- Hexadecimal integer constant : Hexadecimal integer constant takes values from 0 to 15. The value will be preceded by 0x. For example, 0x123
Description
Floating point integer constant represents a real integer value i.e it takes fractional, decimal and integer values also.
- float : Floating point numbers are defined using "float" keyword and takes 2 bytes of memory.
- double : "double" keyword is used when precision provided by the float is not sufficient and takes 4 bytes of memory.
- long double : "long double" keyword is used to extend further more compared to double and takes 8 bytes of memory.
Conceptual
figure
Description
A character constant is an alphabet, a digit or a single special symbol.
- Character constant can hold a single character at a time and value should be enclosed in single quotes' '. For example, char c='A'.
- Format specifier for character constant is "%c".
Example
[c]
#include<stdio.h>
int main()
{
char cvar = 'A';
printf("Character is : %c", cvar);
return(0);
}[/c]
Description
String constant is same as character constant and can be enclosed in double quotes" ". There is no special datatype for string.
For example, char area= "A"; Here "char" is only used as datatype. There is also another constant which can be used in C-language.
Backslashes
These constants should be started with backslash.
| Symbol | Backslash symbol |
|---|---|
| \b | Backspace |
| \v | Vertical tab |
| \" | Double quote |
| \r | Carriage return |
| \t | Horizontal tab |
| \f | Form feed |
| \\ | Backslash |
| \? | Question mark |
| \a | Alert or bell |
| \' | Single quote |
| \n | New line |
Example
[c]
#include<stdio.h>
#include<conio.h>
int main()
{
const int length=100; /*integer constant*/
const float number=22.7; /*float constant*/
const char c=‘a’; /*char constant*/
const char str[10] = “ABC”; /*string constant*/
const char backslash_char = ‘\?’; /*special char cnst*/
printf(“value of length :%d \n”, length );
printf(“value of number : %f \n”, number );
printf(“value of c : %c \n”, c);
printf(“value of string : %s \n”, str);
printf(“value of backslash_char : %c \n”, backslash_char);
}[/c]
Key Points
- C Constants cannot be modified.
- Integer, float, character, backslash and string are C constants types.
Programming
Tips
Always enclose string constants in double quotes only, otherwise it is considered as character value.