Constants

Constants are static values which do not change during the execution of the program.

There are two types of constants. They are :

1. Numeric  Constants

2. String Constants

 1. Numeric Constants

The numeric constants are divided into :

1.1 Numeric Real Constants

1.2 Numeric Integer Constants

1.1 Numeric Real Constants  

 A numeric real constant is one which is written using the digits 0,1,2,3,4,5,6,7,8,9 and the decimal point.

• The signs '+' or '-' can appear before the constant
• In the absence of the sign, the number is assumed to be positive.

Table C 2.7 Numeric Real Constants

Valid                                                                       Invalid 

 Numeric Real Constants                                         Numeric Real Constants

                                                            Constants                  Invalid reason

16.291                                                 16.291                 Blank character is not allowed                                                    

0.241                                                   16.2,91                Comma is not permitted

-29.0                                                    25.1+0                a sign (+) can appear only before the constant

205.205

2.5E +2

1.2 Numeric Integer Constants

Numeric integer constants are those numeric values that are written using decimal digits 0,1,2,3,4,56,7,8,and 9.

• Numeric integer constant is a whole number written without decimal point.
• The signs '+' and '-' can appear before the constants.
•  In the absence of sign, the number is assumed to be positive. 
•  The constants should not contain any special character.
• The valid range of numeric constants is from -32768 to 32767.

Example 4
Table C 2.8 Numeric Integer Constants

Valid numeric                                               Invalid

integer constants                                          numeric integer constant

                                                                   constant            invalid reason

-32767                                                       120.5               contains a blank

 0                                                               10,120            use of comma is not permitted

125                                                            20.05           decimal point is not allowed value out of range

31291                                                        -32769 

2. String constants            

A sequence of a set of characters enclosed in a pair of double quotes is known as a string (or literal) constant.

• The string can contain either alphabets or numeric constants or special characters or combination of them.
• Blank spaces can be freely instated any where in a string with a pair of double quotes.
• Some system of BASIC don't accept double quote symbol as a part of a string.

Example 5

"We are learning about string constants"               

"MY HOBBY & AMBITION ARE different"

"Rs. 2053"

"2053/04/14"

"SLC Examination"

"My" best "friend  is Raghav" (some system may not accept this example as a valid string)