Practical Guide to Using Static Variables in C++ Programs

Variable(name given to memory location):

• The variables can be changed during the execution of a program.
• The value of a variable is associated with a data type, which determines the kind of data it can hold (e.g., integers, floating-point numbers, characters).

 Declaring Variables:

// Declaring a single variable

type variable_name;

// Declaring multiple variables:

type variable1_name, variable2_name, variable3_name;

Rules For Declaring Variable

• starts with a letter (lower ,upper,underscore)
• Suceeding characters can be letters, numbers, or underscores.
• The variables are case-sensitive
• It should not be C++ keyword (reserved word like int, for, while, etc.).
• The  variable name can be:

camel case: typically used for variable names in c++ (e.g., firstname, studentage).

snake case: another option (e.g., first_name, student_age).

uppercase: constants are often written in uppercase letters with underscores separating words (e.g., max_size).

Valid variable names:

———————————–

int a;   //can be letters

int _pa; //can be underscores  

int a55;//can be letters   

invalid variable name

————————————

int 89; Should not be a number  

int a b; //Should not contain any whitespace   

int double;

Variable declaration and definition:

————————————————————

// C++ program to show difference between

// definition and declaration of a

// variable

#include <iostream>

using namespace std;

int main()

{

    int a; // declaration part

    a = 5;//initialization

    int myvariable= 20;    //definition = declaration + initialization

    char b56 = ‘b’;/*declaration and definition */

float c;// declaration+definition and assigns some garbage value

    // multiple declarations and definitions

    int _myvariable, _myvariable1, e;

    // Let us print a variable

    cout << a123 << endl;

    return 0;

}

Types of Variables:

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There are three types of variables based on the scope of variables in C++

Local Variables

Instance Variables

Static Variables

Program that differentiates the local variables ,global variables and static variables

#include<iostream.h>

class vehicle

{

public:

static int a;  //  static varaiable

int b; // global variable

public:

func()

{

int c;  // local variable

}

};

1. Local Variables:

• Definition: Variables declared inside a block (e.g., a function or loop) are local to that block.
• Scope: Limited to the block in which they are defined.
• Lifetime: Created when the block is entered and destroyed when the block exits.
• Storage: Stored in the stack memory.

2. Global Variables

1. Scope:

1. • Global variables are accessible in all functions and blocks within the file in which they are declared.
   • If you use multiple files, you can use the extern keyword to access global variables across files.

2. Lifetime:

1. • Global variables exist for the entire duration of the program’s execution.

3. Default Value:

1. • Automatically initialized to 0 for basic data types (e.g., int, float).

4. Storage:

1. • Stored in the global memory section.

5. Modification:

1. • Any function can modify a global variable unless it is declared as const

3. Static Variables in Local Scope

• Definition: Local variables declared with the static keyword.
• Scope: Limited to the block in which they are defined (like local variables).
• Lifetime: Exist for the lifetime of the program. Their value persists between function calls.
• Initialization: Initialized only once when the function is called for the first time. Default initialization is 0 if no value is provided.

Comparison of Local, Global, and Static Variables