How To Declare Variables In Dev C++

Posted By admin On 03.01.21

Dec 12, 2019  A C program might contain more than one compilation unit. To declare an entity that is defined in a separate compilation unit, use the extern keyword. The information in the declaration is sufficient for the compiler, but if the definition of the entity cannot be found in the linking step, then the linker will raise an error.

Rules of Declaring variables in C A variable name can consist of Capital letters A-Z, lowercase letters a-z, digits 0-9, and the underscore character. The first character must be a letter or underscore. Blank spaces cannot be used in variable names. When declaring variables with var and let, we can optionally initialize the variables at the point of declaration: var a = 2; var b = 3; Declaring variables with the var keyword. When you declare a variable using the var keyword, the scope is as follows: If the variable is declared outside of any functions, the variable is available in the.

A variable is a name which is associated with a value that can be changed. For example when I write int num=20; here variable name is num which is associated with value 20, int is a data type that represents that this variable can hold integer values. We will cover the data types in the next tutorial. In this tutorial, we will discuss about variables.

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Syntax of declaring a variable in C++

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For example:

We can also write it like this:

Types of variables

Variables can be categorised based on their data type. For example, in the above example we have seen integer types variables. Following are the types of variables available in C++.

int: These type of of variables holds integer value.

Dev C++ Variables

char: holds character value like ‘c’, ‘F’, ‘B’, ‘p’, ‘q’ etc.

bool: holds boolean value true or false. 3u tools 11 restore.

double: double-precision floating point value.

float: Single-precision floating point value.

Types of variables based on their scope

Before going further lets discuss what is scope first. When we discussed the Hello World Program, we have seen the curly braces in the program like this:

Any variable declared inside these curly braces have scope limited within these curly braces, if you declare a variable in main() function and try to use that variable outside main() function then you will get compilation error.

Now that we have understood what is scope. Lets move on to the types of variables based on the scope.

1. Global variable
2. Local variable

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Global Variable

A variable declared outside of any function (including main as well) is called global variable. Global variables have their scope throughout the program, they can be accessed anywhere in the program, in the main, in the user defined function, anywhere.

Lets take an example to understand it:

Global variable example

Here we have a global variable myVar, that is declared outside of main. We have accessed the variable twice in the main() function without any issues.

Output:

Local variable

Local variables are declared inside the braces of any user defined function, main function, loops or any control statements(if, if-else etc) and have their scope limited inside those braces.

Local variable example

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Output:
Compile time error, because we are trying to access the variable myVar outside of its scope. The scope of myVar is limited to the body of function myFuncn(), inside those braces.

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Can global and local variable have same name in C++?

Lets see an example having same name global and local variable. Studio one 4.5 plugin manager.

Output:

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As you can see that when I changed the value of myVar in the main function, it only changed the value of global variable myVar because local variable myVar scope is limited to the function myFuncn().