What are Variables in C? Meaning, Usage, Declaration, Examples

What are Variables in C?

A variable in C acts like a container that stores information or data values. Once the data values are stored in the variable, we can use this variable as many times as we want. A variable in C has some characteristics, like its lifetime, scope, and range of values it can store.

A variable in C can take different types of values like integer, character, string, float, and double values, which are important parts of the GATE CSE syllabus. Each variable is associated with a data type that allows for storing values of a particular type. 

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Variable in C Meaning

The name of a memory address we use to store data is all that a variable means. In C or any other programming language, we can modify a variable's value and reuse it several times. Variables play an integral part in any source code. Once a variable is declared, we can perform multiple tasks using it within the same source code.

Variable in C Example

As we already know, every variable declared in the program is associated with a data type. It may take a range of values depending on the data type. Along with the data type, it may also use storage classes that precisely define the scope and lifetime of a variable. And these data types are essential as per the GATE exam.

Let us see an example of variables in C:

#include<stdio.h>

int main()

{

int day= 12;

char grade= 'A';

float marks= 98.7;

string name="Saif";

printf("%d\n%c\n%f\n%s\n", day, grade, marks, name);

return 0;

}

The above program declares and initializes four variables that store data values according to the associated data type. The variables here are day, grade, marks, and name.

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Use of Variable in C

Knowing the meaning and definition of a variable, one might wonder what is the use of defining the variables in C? Well, for the efficient working and execution of the program, we use variables. Every variable has a type and size.

The importance of variables can also be seen in the GATE question papers. Variables store data that the programmer or user can later use to complete the execution of a particular task or code.

Declaration of Variable in C

Variable declaration in C provides the compiler with the credibility that a particular storage area is assigned some name along with the size and type.

Initialization of Variable in C

One can also initialize the value of a variable that is assigning a valid value

(belonging to the specified type and size of the variable) to the variable is termed initialization. The syntax for initializing a variable is: type variable name= value; 

Here int and float represent the type of variable, respectively, and marks and weight represent variables’ names with values assigned to them.

Data Types of Variables in C

In C, variables are divided based on various categories based on size, scope, lifetime data types, etc. Based on data types, we have two categories:

• Primitive data types
• User-defined data types
• Derived data types

1. Primitive data types: It is mandatory to assign a data type to a variable in C, which defines the type of data stored under the variable name. Primitive data types in C are shown in the below table:

2. User-defined data types: These data types have been designed to ease the user's purpose. In C programming language, we have the following three types of user-defined data types:

• Structure
• Union
• Enum

3. Derived data types: In C, we have derived data types that can contain multiple homogenous data at once. Following are the derived data types in C:

• Array
• Functions
• Pointers
• Storage classes of variables in C

Every variable in C has characteristics like the data type, scope lifetime, etc. The storage classes deal with the scope and lifetime of the variable. The storage classes are mainly classified into four categories:

• Auto storage class
• Register storage class
• Static storage class
• Extern storage class

Auto Storage Class

All the local variables are auto variables by default. Auto varibales are different from the constants in a C program.

The default contains a garbage value if an auto variable is not initialized. For every function call, the auto variable is recreated and re-initialized. It has local scope.

Register Storage Class

The keyword register is just a request to the compiler to allocate memory in the registers instead of RAM; if the accessible registers are available, then memory will be allocated in the registers. Otherwise, it will be allocated in the RAM only.

Static Storage Class

For static variables, the memory will be allocated only once at compile time; if it is not initialized, the default contains zero. A static variable will persist in its value even after the destruction of several function calls.

Extern Storage Class

The variable declared extern would not be allocated any memory. These are also sometimes used in questions formation of GATE CSE exam. It will use the external memory (global variables).