This document discusses different types of constants and variables in C programming. It describes integer, real, and character constants, and rules for constructing each type. It also discusses primary and secondary constants. The document then covers variables, including naming conventions, case sensitivity, declaring variables to reserve memory space, and using the assignment statement to assign values.

2. Types of constants
Constants
Primary Secondary
Constants Constants
Integer Constants Array
Real Constants Pointer
Character Structure
Constants Union
Enum. etc

3. Rules for Constructing Integer Constants
● An integer constant must have at least one digit.
● It must not have a decimal point.
● It can 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 an integer constant.
● The allowable range for integer constants is -32768 to 32767.
● Ex.: 426
+782
-8000
-7605

4. Rules for Constructing Real
Constants
● A real constant must have at least one digit.
● It must have a decimal point.
● It could be either positive or negative.
● Default sign is positive.
● No commas or blanks are allowed within a real
constant.
● Ex.: +325.34
426.0
-32.76
-48.5792

5. Rules for Constructing Character
Constants
● A character constant is a single alphabet, a single digit
or a single special symbol enclosed within single
inverted commas. Both the inverted commas should
point to the left. For example, ’A’ is a valid character
constant whereas ‘A’ is not.
● The maximum length of a character constant can be 1
character.
● Ex.: 'A'
'I'
'5'
'='

6. Variables in ‘C’
● Naming Variables
● Declaring Variables
● Using Variables
● The Assignment Statement

7. What Are Variables in C?
● Variables in C have the same meaning as variables in algebra. That
is, they represent some unknown, or variable, value.
x=a+b
z + 2 = 3(y - 5)
● Remember that variables in algebra are represented by a single
alphabetic character.

8. Naming Variables
● Variables in C may be given representations containing multiple
characters. But there are rules for these representations.
● Variable names (identifiers) in C
○ May only consist of letters, digits, and underscores
○ May be as long as you like, but only the first 31 characters are significant
○ May not begin with a digit
○ May not be a C reserved word (keyword)

9. Naming Conventions
● C programmers generally agree on the following conventions for
naming variables.
○ Begin variable names with lowercase letters
○ Use meaningful identifiers
○ Separate “words” within identifiers with underscores or mixed upper and
lower case.
○ Examples: surfaceArea surface_Area surface_area
○ Be consistent!

10. Reserved Words (Keywords) in C
● auto break ● int long
● case char ● register return
● const continue ● short signed
● sizeof static
● default do
● struct switch
● double else ● typedef union
● enum extern ● unsigned void
● float for ● volatile while
● goto if

11. Naming Conventions (con’t)
● Use all uppercase for symbolic constants (used in #define
preprocessor directives).
● Note: symbolic constants are not variables, but make the program
easier to read.
● Examples:
● #define PI 3.14159
● #define AGE 52

12. Case Sensitivity
● C is case sensitive
○ It matters whether an identifier, such as a variable name, is uppercase or
lowercase.
○ Example:
area
Area
AREA
ArEa
are all seen as different variables by the compiler.

13. Which Are Legal Identifiers?
● AREA area_under_the_curve
● 3D num45
● Last-Chance #values
● x_yt3 pi
● num$ %done
● lucky***

14. Declaring Variables
● Before using a variable, you must give the
compiler some information about the variable;
i.e., you must declare it.
● The declaration statement includes the data
type of the variable.
● Examples of variable declarations:
● int meatballs ;
● float area ;

15. Declaring Variables (con’t)
● When we declare a variable
○ Space is set aside in memory to hold a value of the specified data
type
○ That space is associated with the variable name
○ That space is associated with a unique address
○ Unless we specify otherwise, the space has no known value.
● Visualization of the declaration
○ int meatballs ;
meatballs
garbage
FE07 int