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Constants in C Programming | C Programming


Constants in C Programming: -

       Constants in C refers to fixed valued that do not change during the execution of a
program. const is the keyword and its used to declare constants.

A constant value is the one which does not change during the execution of a program.
C supports several types of constants.
·        Integer Constants
·        Real Constants
·        Single Character Constants
·        String Constants

A constant value is the one which does not change during the execution of a program.  C supports several types of constants.     
  • Integer Constants   
  • Real Constants   
  • Single Character Constants   
  • String Constants     


Integer Constants 

An integer constant is a sequence of digits. There are 3 types of integer's namely decimal integer, octal integers and hexadecimal integer.     

Decimal Integers: 
Consists of a set of digits 0 to 9 preceded by an optional + or - sign. Spaces, commas and non-digit characters are not permitted between digits. Examples for valid decimal integer constant are:      
  • 123   
  • -31   
  • 0   
  • 562321  
  • + 78    

Some examples for invalid integer constants are:    
  • 15 750   
  • 20,000   
  • Rs. 1000     


Octal Integers: 

Constant consists of any combination of digits from 0 through 7 with an O at the beginning. Some examples of octal integers are:    
  • O26   
  • O   
  • O347  
  • O676     


Hexadecimal integer:
Constant is preceded by OX or Ox, they may contain alphabets from A to F or a to f. The alphabets A to F refer to 10 to 15 in decimal digits. Examples of valid hexadecimal integers are:       
  • OX2  
  • OX8C  
  • OXbcd   
  • Ox     


Real Constants     

Real Constants consists of a fractional part in their representation. Integer constants are inadequate to    represent quantities that vary continuously. These quantities are represented by numbers containing    fractional parts like 26.082. Examples of real constants are:    
0.0026    -0.97    435.29    +487.0   

Real Numbers can also be represented by exponential notation. The general form for exponential notation is mantissa exponent. The mantissa is either a real number expressed in decimal notation or an integer. The exponent is an integer number with an optional plus or minus sign.     
A Single Character constant represent a single character which is enclosed in a pair of quotation    symbols.   

Example for character constants are:    

'5'    'x'    ';'    ' '    

All character constants have an equivalent integer value which is called ASCII Values.     

String Constants     

A string constant is a set of characters enclosed in double quotation marks. The characters in a string constant sequence may be an alphabet, number, special character and blank space. Example of string constants are   
"1234"   
"God Bless"   
"!.....?"     

Backslash Character Constants [Escape Sequences]     
Backslash character constants are special characters used in output functions.  Although they contain    two characters they represent only one character. Given below is the table of escape sequence and them meanings.                
Constant                 Meaning               
'\a'                         Audible Alert (Bell)              
'\b'                         Backspace               
'\f'                          Form feed              
'\n'                         New Line              
'\r'                         Carriage Return              
'\t'                         Horizontal tab             
'\v'                         Vertical Tab             
'\''                          Single Quote             
'\"'                         Double Quote              
'\?'                         Question Mark              
'\\'                         Back Slash             
'\0'                         Null  


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