Variables in C Language

In this tutorial, we will be covering Variables in detail in C language.

When we want to store any information(data) on our computer/laptop, we store it in the computer's memory space. Instead of remembering the complex address of that memory space where we have stored our data, our operating system provides us with an option to create folders, name them, so that it becomes easier for us to find them and access them.

Similarly, in C language, when we want to use some data value in our program, we can store it in a memory space and name the memory space so that it becomes easier to access it.

The naming of an address is known as a variable. Variable is the name of the memory location. Unlike constant, variables that are changeable, we can change the value of a variable during the execution of a program. A programmer can choose a meaningful variable name. Example: average, height, age, total, etc.

Datatype of Variable

A variable in C language must be given a type, which defines what type of data the variable will hold.

It can be:

• char: Can hold/store a character in it.

• int: Used to hold an integer.

• float: Used to hold a float value.

• double: Used to hold a double value.

• void

Rules to name a Variable

1. Variable name must not start with a digit.

2. The variable name can consist of alphabets, digits, and special symbols like underscore _.

3. Blank or spaces are not allowed in the variable name.

4. Keywords are not allowed as a variable name.

5. Upper and lower case names are treated as different, as C is case-sensitive, so it is suggested to keep the variable names in lower case.

Declaring, Defining and Initializing a variable

Declaration of variables must be done before they are used in the program. The declaration does the following things.

1. It tells the compiler what the variable name is.

2. It specifies what type of data the variable will hold.

3. Until the variable is defined the compiler doesn't have to worry about allocating memory space to the variable.

4. The declaration is more like informing the compiler that there exists a variable with the following datatype which is used in the program.

5. A variable is declared using the extern keyword, outside the main() function.

extern int a;
extern float b;
extern double c, d;

Defining a variable means the compiler has to now assign storage to the variable because it will be used in the program. It is not necessary to declare a variable using extern a keyword if you want to use it in your program. You can directly define a variable inside the main() function and use it.

To define a function, we must provide the datatype and the variable name. We can even define multiple variables of the same data type in a single line by using a comma to separate them.

int a;
float b, c;

Initializing a variable means providing it with a value. A variable can be initialized and defined in a single statement, like:

int a = 10;

Let's write a program in which we will use some variables.

#include <stdio.h>

// Variable declaration(optional)
extern int a, b;
extern int c;

int main () {

    /* variable definition: */
    int a, b;
 
    /* actual initialization */
    a = 7;
    b = 14;
    /* using addition operator */
    c = a + b;
    /* display the result */
    printf("Sum is : %d \n", c);
    
    return 0;
}

Sum is : 21

You must be thinking how does this printf() works, right? Do not worry, we will learn about it along with other ways to input and output data in C language in the next tutorial.

Difference between Variable and Identifier?

An Identifier is a name given to any variable, function, structure, pointer, or any other entity in a programming language. While a variable, as we have just learned in this tutorial is a named memory location to store data that is used in the program.

// a variable
int studytonight;
// or, a function
int studytonight() { 
    .. 
}

// int variable
int a;
// float variable
float a;

Another great analogy to understand the difference between Identifier and Variable is:

You can think of an Identifier int x to be a variable's name, but it can also be a function's name int x() { } and still, be an identifier.

Just like Obama is a name of a person, but also the name of a foundation.

Frequently asked questions

Ques 1: Write the proper declaration of the character variable color, name.

The proper declaration of the given two character variables will be as follows:

char color;

char name;

Ques 2: What is Variable?

A variable is mainly a data name that is mainly used to store the data value. It is important to note that it may take different values at different times during the execution of the program.

Ques 3: In the given below choose the invalid variable names:

• area

• char

• Average dist

• B2

• distance

• age1

• Total

• Sen$

In the above question invalid variable names are:

Sen$: because $ sign is not allowed in the name of the variable.

Average dist: because whitespace/blankspace is not allowed.

char: It is an invalid name of the variable because it is a keyword.

Conclusion

This tutorial was all about the variables in the C language. We have covered what exactly a variable is, how it is declared and initialized in C. We have covered some rules that you should follow while writing the name of the variable. We have also covered points of difference between a variable and an identifier.