Variables
A variable is a container which holds the data or the value the user gives. variables are memory locations in a computer's memory to store data. variable is varying it can take different values during times during execution.
Every variable in C has three most fundamental attributes. They are:
Name
Value
Address
Guidelines for naming a variable:
A variable must begin with either a letter or an underscore(_).
C is a case sensitive, hence upper and lower case letters are treated as different. For example sum is different SUM
Only “ _ “ is used as a special symbol, other symbols are not permitted.
variable should not be a keyword.
Valid Variables:
Sum, count, area, roll_no
Invalid Variables:
roll no - No blank spaces are allowed
%marks - Special symbols are not allowed
int - Keyword cannot be a variable.
Declaration of variable:
A variable declaration tells the compiler where and how much storage is needed to create the variable. a variable definition specifies a data type and contains a list of one or more variables of that type.
Syntax: data_type variable1, variable2
variable1 - name of the variable
variables are separated by comma. The statement should always end with a semicolon.
Example: int radius, count
Assignment/Initialization of variables
Values can be assigned with a value using assignment operator (=)
Syntax: varible_name = constant
Example: sum =100;
The value of a variable can be assigned during the declaration of the variable. This process is called initialization. C variables declared can be initialized with the help of assignment operator ‘=’.
syntax: data_type variable_name = constant;
Example: int roll_no = 596403
Sample program of declarations, assignment and values stored in variable.
#include <stdio>
int main() {
//Declaration
int sum1, sum_2, count;
float avg;
//Declaration and initialization
char letter = ‘A’;
//Assign values
sum1 = 200;
sum_2=30;
count = sum1+sum_2;
avg = count/2;
//Printing values
printf(“The sum of two number is: %d”, count);
printf(“The average of two number is: %f”, avg);
printf(“Character is: %c”, letter);
return 0;
}
Getting input through the user:
The data can be read from the user through the keyboard using scanf function.
syntax: scanf(“control string” ,&variable1, &variable2);
The control string represents the type of the variables specified. “&” symbol specifies the address of the variable.
Example:
scanf(“%d%f” , &sum, &avg);
where,
%d refers to integer value
%f refers to float value
Sample program using scanf function:
#include <stdio>
int main(){
int length, breadth, area;
printf(“Enter the length and breadth of a rectangle”);
scanf(“%d%d”, &length, &breadth);
area = length*breadth;
printf(“Area of a rectangle is”, area);
return 0;
}
Constant variables:
Variables having an unchanged value during the execution of the program are referred to as constant Variables. A constant variable can be declared by using the keyword “const”.
Example: const int value = 100;
Volatile Variable:
variables which can be changed at any time by some external sources from outside or same program are called volatile variables.
Syntax: volatile datatype variable;
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