Learn C, C++ Programming

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• C Constants are also like normal variables. But, only difference is, their values can not be modified by the program once they are defined.
• Constants refer to fixed values. They are also called as literals
• Constants may be belonging to any of the data type.

• Syntax:

const data_type variable_name; (or) const data_type *variable_name;

……

Types of C constant:

1. Integer constants
2. Real or Floating point constants
3. Octal & Hexadecimal constants
4. Character constants
5. String constants
6. Backslash character constants

S.no	Constant type	data type	Example
1	Integer constants	int unsigned int long int long long int	53, 762, -478 etc  5000u, 1000U etc 483,647 2,147,483,680
2	Real or Floating point constants	float doule	10.456789 600.123456789
3	Octal constant	int	013          /* starts with 0  */
4	Hexadecimal constant	int	0x90        /* starts with 0x */
5	character constants	char	‘A’   ,   ‘B’,     ‘C’
6	string constants	char	“ABCD”   ,   “Hai”

Rules for constructing C constant:

1. Integer Constants in C:

• An integer constant must have at least one digit.
• It must not have a decimal point.
• It can either be positive or negative.
• No commas or blanks are allowed within an integer constant.
• If no sign precedes an integer constant, it is assumed to be positive.
• The allowable range for integer constants is -32768 to 32767.

2. Real constants in C:

• A real constant must have at least one digit
• It must have a decimal point
• It could be either positive or negative
• If no sign precedes an integer constant, it is assumed to be positive.
• No commas or blanks are allowed within a real constant.

3. Character and string constants in C:

• A character constant is a single alphabet, a single digit or a single special symbol enclosed within single quotes.
• The maximum length of a character constant is 1 character.
• String constants are  enclosed within double quotes.

4. Backslash Character Constants in C:

• There are some characters which have special meaning in C language.
• They should be preceded by backslash symbol to make use of special function of them.
• Given below is the list of special characters and their purpose.

#include <stdio.h>

void main()
{
   const int  height = 100;                /*int constant*/
   const float number = 3.14;              /*Real constant*/
   const char letter = 'A';                /*char constant*/
   const char letter_sequence[10] = "ABC"; /*string constant*/
   const char backslash_char = '?';      /*special char cnst*/

   printf("value of height    : %d n", height );
   printf("value of number : %f n", number );
   printf("value of letter : %c n", letter );
   printf("value of letter_sequence : %s n", letter_sequence);
   printf("value of backslash_char  : %c n", backslash_char);
}

Output:

value of height : 100 value of number : 3.140000 value of letter : A value of letter_sequence : ABC value of backslash_char : ?

2. Example program using #define preprocessor directive in C:

#include <stdio.h>

#define height 100
#define number 3.14
#define letter 'A'
#define letter_sequence "ABC"
#define backslash_char '?'

void main()
{

   printf("value of height    : %d n", height );
   printf("value of number : %f n", number );
   printf("value of letter : %c n", letter );
   printf("value of letter_sequence : %s n", letter_sequence);
   printf("value of backslash_char  : %c n", backslash_char);

}

Output:

value of height : 100 value of number : 3.140000 value of letter : A value of letter_sequence : ABC value of backslash_char : ?

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