This document discusses constants, variables, and data types in C programming. It defines tokens and keywords as the basic units, and explains constants and variables as values that either remain fixed or can change. Various data types are covered, including primary, user-defined, and derived types, along with modifiers that alter storage capacity. Rules for variable names and declarations are provided. The document also discusses assigning values to variables through constants, multiple assignments, and initialization.

1. Constants, Variables and Data Types
Topics
 Token, Keyword, Identifier
 Constant, Variable
 Data types

2. Token and Keyword
 Token- In a C program the smallest individual units
are known as C tokens. C has six types of tokens.
1. Keyword- float, int, while
2. Identifier- main, amount
3. Constant- 10.5, 10
4. String- “ABC”, “Khulna”
5. Special symbol- [ ], { }
6. Operator- +,-,*
 Keyword- Keywords are the reserve words which
have fixed meanings and that cannot be changed.
Ex- float, double, while, char, do, if, else

3. Identifier, Constant
 Identifier- Identifiers refer to the names of variables,
functions and arrays.
 Constant- Constants in C refer to fixed values do
not change during the execution of a program. Ex-
123, -0.75, ‘X’, “CSE”
 Process of declaring constant:
1. #define: #define const_name value
Ex: #define MAX 100
2. const: const data_type const_name = value;
Ex: const int MAX=100;

4. Variable
 Variable- A variable is a data name that may be
used to store data value. A variable may take
different values at different times during execution.
 Rules of variable name:
1. It must begin with a letter. Some systems permit
underscore as the first character.
2. ANSI standard recognizes a length of 31
characters. But it should normally in between 8 char.
3. Uppercase and lowercase are different.
4. Variable name should not be a keyword.
5. White space is not allowed.

5. Data Types
 Primary data types- character, Integer, Float,
Double
 User-defined data types- Structure, Union, Class,
Enumeration
 Derived data types- Array, Function, Pointer,
Reference

6. Modifier or Qualifier
 Modifier- The keyword like short, long, unsigned,
signed can change the data storage capacity of the
variable. So they are called modifier or qualifier.
 Type Size (bits) Range
char 8 -128 to 127
int or short int 16 -32768 to 32767
unsigned int 16 0 to 65535
short int 8 -128 to 127
long int 32 -2147483648 to 2147483648
float 32 3.4E-38 to 3.4E+38
double 64 1.7E-308 to 1.7E+308
long double 80 3.4E-4932 to 3.4E+4932

7. Variable Declaration
 Declaration does two things:
1. It tells the compiler what the variable name
is.
2. It specifies what type of data the variable
will hold.
 The declaration of variables must be done
before they are used in the program.
 Rule: Data_type Var_name;
 Ex: int x, y;
float area;

8. Assigning values to Variables
 Rule: var_name = constant;
Ex: balance = 1277.50;
ch = ‘Y’;
 C permits multiple assignments in one line.
Ex: length=10; height=5;
 It is also possible to assign a value to a variable at
the time of variable declaration.
Ex: int x = 100;
 C permits the initialization of more than one
variables in one statement using multiple
assignment operators.
Ex: x = y = z = 100;