C variable

The target

In this article, you’ll learn about the C variable that allows you to manipulate data in your program.

Introducing the C variable

A program consists of data and a set of instructions for processing that data. Data can be numbers and characters. To store data in a program, you need to use variables.

Variables allow you to store data during program execution.

Declare a variable

Before you can use a variable, you need to declare it. Variable declarations serve two purposes:

  • Define the name of the variable.
  • Defines the types of data a variable can store.

For example, the following statement declares a variable:

int age;

The int keyword tells C that the variable will hold an integer value. The variable name is age. The semicolon (;) End statement.

The general form of a variable declaration is:

type variable_name;

The type can be any valid type in C.

When you declare a variable:

  • C reserves a space in memory to hold the value of a variable. The size of memory depends on the type of value the variable is to store.
  • C also allocates a memory space associated with variable names and unique addresses.

Variables can be declared at any point in the program before they are used. It’s a good practice to declare variables closest to where they were first used.

Variable names in C should follow the following rules:

  • Variable names can contain letters, digits, and underscores. The first character of a variable name must be a letter or underscore. However, you should avoid using the underscore (_) as the first letter, because it may conflict with standard system variables.
  • According to ANSI C, variable names should have a maximum of 31 characters.
  • In addition, variable names cannot be the same as reserved words or keywords in C.

Keywords in C are shown in the following table:
auto break int reurn
case char register signed
const continue short static
default do sizeof switch
double else struct union
enum extern typedef void
float for unsigned while
goto if volatile

If you have multiple variables of the same type, you can declare them in a single statement. Such as:

int age, min_age, max_age;

Initialize a variable

For convenience, C allows variables to be initialized when they are declared. For example,

int age= 1;

Char ch = 'a';

It is a good practice to put initialized variables on a separate line and add descriptive comments explaining why the variable was initialized to a particular value. Such as:

int speed = 60; // Minimum speed limit on motorway

Variable assignment

To assign a value to a variable, use the assignment operator (=). Such as:

int age= 1; int speed_limit; age= 2; speed_limit = 60; // 60 kilometers per hourCopy the code

How it works.

  • First, declare two variables age and speed_limit.
  • Second, assign the age variable to 2 and the speed_limit variable to 50.

In addition to values, you can assign the value of one variable to another. Such as:

int revenue = 100, cost = 90; int profit; profit=revenue-cost; / / 10Copy the code

conclusion

  • Variables store data during program execution.
  • Be sure to declare a variable before you use it.
  • A variable declaration includes the data type and variable name that the variable will hold.
  • You can assign an initial value to a variable during the declaration.
  • Assign a value to a variable using the assignment operator (=).