Constants:
Constants in C refer to fixed values that do not change during the execution of the program.
Constants are classified as shown below.
(i). Integer Constants :
An integer constant refers to a sequence of digits without any decimal point. There are three types of integer constants namely decimal integer, octal integer and hexadecimal integer.
Decimal/Integer constant: It consists of set of digits 0 through 9, preceded by an optional – or + sign. No special symbol and spaces is allowed between digits. Examples : 123, -321, +78
Octal Integer constant : It consists of set of digits 0 through 7, preceded with 0. No special symbol and spaces is allowed between digits. Examples : 037, 0435
Hexadecimal Integer constant : It consists of set of digits 0 through 9, and A to F or a to f, preceded with 0x or 0X. No special symbol and spaces is allowed between digits. Examples: 0x37, 0x435A
(ii). Real Constants:
Numbers that contain fractional parts and whose value does not change. Such numbers are called real (floating point) constants. It is possible to represent real constant number by omitting digits before decimal point or digits after the decimal point. Examples: 0.0083 435.56 .345 215.
Real number may also be expressed in exponential (Scientific) notation as shown below:
Example: 215.15 can be written as 2.1515e2. (Mantissa, Base, Exponent).
(iii). Single Character Constants:
Any character enclosed in single quotes is considered as single character constant.
Examples: ‘5’, ‘x’
The ‘C’ Programming Language supports backslash character constants that can be used in output functions along with the string. These constants have predefined meaning and they are treated as single character constant.
(iv). String Constant / Strings:
Any sequence of characters enclosed in double quotes is considered as string constant.
Examples: “welcome” , “134”.
Note: The ‘a’ is character constant, where as “a” is string constant.
(v). Boolean constants:
The 0 ( false) and 1 (true) is called as Boolean constant.
Variables:
• It is an identity for a memory cell, which stores input values, computational values and output values.
• It is named as variable because, its value changes continuously throughout program execution.
• The variable declaration specifies to compiler about what type of value is stored in the variable and also specifies about list of variables used in the program.
Variable Representation:
A variable is a location in memory that is identified by a name and address and can store value of a particular type as shown below.
Example: int sum=21;
Rules for declaring Variable Name :
1. An variable name must consist of only alphabetic character , digits, and underscore.
2. First character must be alphabetic character or under score and should not be a digit.
3. Second character onwards can be alphabetic character or digit or under score.
4. Variable name can be up to 31/63 characters depending on the system.( first 8 characters are significant)
5. It cannot be same as key word / reserved word.
6. May not have a white space or any other special symbol except under score.
7. C – language is Case-sensitive. So that, the variable name should be defined specifically to uppercase or
lower case letters.
Examples for User defines Identifiers :
Valid identifiers In Valid identifiers
Rollnumber, Name 4you, Do today, #welcome
Subject1, marks auto, int
College_name
Declaration of a Variable:
1. Single variable of specified data type can be declared as
data_type_name var_name; Example: int tot_marks;
2. Multiple variables of same data type can be declared as
data_type_name var_name1, var_name2,….; Example: int a, b, c;
Initialization of Variables:
The variables can be initialized by using assignment operator as shown below.
1. The variable declaration and inialization can be specified separately as shown below
Syntax :
data_type_name var_name;
var_name= Initial_value;
Example: int sum;
sum=0;
2. The variable declaration and inialization can be specified combinely as shown below
Syntax :
data_type_name var_name = Initial_value;
Example: int sum=0;
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