C character set

          The character that can be used to form words,number and expressions depend upon the computer on which the program is run.

    The character in C are grouped into the following categories.

• Letters

• Digits

• White spaces

•  Special characters

   Letters:
 

•  Uppercase A to Z. 
•   Lowercase a to z.

 Digits:

•   0 to 9 

White space:

• Blank space
• Horizontal tab 
• Carriage return
• New line
• Form feed

Special characters:

Constants:

•  Constants in C refer to fixed values that do nto change during the execution of a program.
• C supports several type of constants see the primary constants as below.

                       

1. Integer Constants:

• An integer constant refers to a sequence of digits.
• It contains of set of digits,0 to 9, preceded by optional - or + sign.
• It must be have a decimal point.
• valid example: 123 ,  -12  ,  0  ,  +78  ,  654321
• Invalid: 15 750 ,  20,550  ,  $123

2.Real constants: 

•  A real constants refer to a sequence of digits the point.
• Number containing fractional parts like 15.55 such number are called real(or floating) constants.
• Valid e.g. 0.0043

                        -0.75

                       +132.0

• Invalid: 15.750 ,  20,550.33 ,  +$132

3.Single Character constants

• A single character constant contain a single character enclosed within a pair of single quote marks.
• Each character constant represents an integer value.
• e.g :  '5'  ,   'x'  ,   ';'  ,  ' '
• Note that the character constant '5' is not the same as number 5.
• The last constant is a blank space.

character constants have integer value knows as ASCII (American code for information interchange) values.
   
       printf("%d",'a');

       I will print the number 97, the ASCII value of the letter a.

       printf("%d",97);

       It will print the letter 'a'.

4. String Constants:

•  A string constants is a sequence of character enclosed in double quotes.
• The character may be letters,numbers,special character and blank space.

• e.g: "Hello" , "1947" , "welcome" , "5+6"  ,  "x"

•  Character constants ('X') is not equivalent to the single character string constant ("X").
• A single character string constants does not have an equivalent integer value while a character constants has an integer value.