Variables in C - Programming Language

Variables

Variables are the name of a memory location where data is being stored .

int a = 10 ;

Here we are storing the value 10 in a variable named a.

How to visulaise a variable in a place .

• We can imagine a variable as a conatiner in any language where we can store some data and modify that in later down the line in code .

• A variable make it easy for us to access the data we want to access for mathematical operations.

• Lets take an example for better undersatnding :

  lets assume that i want to add some numbers in my c program and then print the result in terminal .
  

  
          int i = 10;
          int j = 20;
          // int k = i + j; 
  
          printf("%d \n", i + j);
  

  • When we run the code and its print the output we get our result , but here we are not able to store that data into something for later use .
  • So we need to store the result in a variable .

Rules for naming variables .

So there are bunch of rules and regulations for naming variables , that one should follow otherwise the compiler will give an error .

• Variables must start with a letter or an underscore ("_").

  It means that if we start the variable name with a number then the compiler will give an error.

   we can make variable name as "_abc" or "abc_" or "abc"  

   but not "1abc" or "@abc" or "abc@" .

• Variables must not contain spaces or commas.

  It means that if we have a variable name which contains spaces then the compiler will give an error.

  we can make variable name as "abc1def" or "abc_def" or "abcdef"  

  but not "abc,def" or "abc def" or "abc@def" .

• Variables must not start with a number.

  It means that if we start the variable name with a number then the compiler will give an error.

  we can make variable name as "abc" or "abc_" or "abc"  

  but not "1abc" or "45abc" or "001_abc@" .

• Variables must not contain any special characters only "_" is allowed .

  It means that if we have a variable name which contains special characters then the compiler will give an error.

  we can make variable name as "abc" or "abc_" or "abc"  

  but not "1abc" or `@abc` or "abc@" .

How to declare a variable .

• We can declare a variable in two ways .
• One is by using the keyword int .
• Another is by using the keyword float .
• we can also use the keyword char .
• we can also use the keyword double .
• All these keywords are used to declare a variable .

Lets take an example for better undersatnding :

    int i = 10;
    float f = 10.5;
    char c = 'a';
    double d = 10.5;

• Here we are declaring a variable named i and assigning it the value 10 .

• Here we are declaring a variable named f and assigning it the value 10.5 .

• Here we are declaring a variable named c and assigning it the value 'a' .

Here all these i , f , c , d are called variables .

• Here all these int , float , char , double are called types of the variable and the type of data they can store , Datatypes.

we would be discussing datatypes in next Module !

How to assign a value to a variable .

• We can assign a value to a variable by using the keyword = .
• datatype variable_name = value_to_be_stores ;

Naming Convention

There are some convention for naming variables .
By following these convention we can make our code more readable and maintainable. Some of the convention are as follows:

• Variable names should be written in lowercase_with_underscore.
• Variable names should not start with a number.
• Variable names should not contain any special characters.
• Variable names should not contain spaces.

• one should mantain a naming system for the variables so that with just one look we can find the variable, and predict here the value is comming from.
  

    int a = 10; ❎
  
    // here we are assigning the value 10 to the variable a , but with more code and more complexity we shall not be able to find the origin of a , and this can take a much time in debugging the code .
  
    int number = 10; ✅
  
    // here by just looking at the variable we can make a idea about the origin of the variable  number that its store some kind of number .
  
    int random_number = 10004546679667677;
  
    // here we can see that the variable `10004546679667677` is comming from the `random_number` variable.
  
    char user_name[20] = "Abhishek Kushwaha";
  
    // here we can see that the variable `Abhishek Kushwaha` is comming from the `user_name` variable.
  
    int user_age = 20;
  
    // here we can see that the variable `20` is comming from the `user_age` variable.
  
  

Comments

[Paul J. Lucas]

You description of declaration isn't right. For example:

int a;

is both a declaration and definition even though there's no assignment. Your example makes it looks like it's the assignment that makes it a definition which isn't true.

Your example of:

printf("%d", i + j);

should be:

printf("%d\n", i + j);

Variables should start with a letter or an underscore.

No. Variables must start with a letter or an underscore. "Should" makes it sound only recommended and not required. You have other uses of "should": they must all be "must."

Your example of:

int user_name = "Abhishek Kushwaha";

is wrong. (You should be able to figure out why.)

[Abhishek kushwaha]

Thanks for The review.
I appreciate your suggestions . 😊

[Dhanashree Rugi]

int user_name = "Abhishek Kushwaha";

"Abhishek Kushwaha" is a character of array hence it has to be declared as,
char string_name[100] = "Abhishek Kushwaha";

[Dhanashree Rugi]

correction please, its array of character not character of array.