C++ Tutorial Index

C++ Tutorial C++ History C++ Installation C++ First Program C++ cin and cout C++ Data type C++ Variable C++ operator C++ Keywords

C++ Control Statements

C++ If C++ Nested if C++ If-else C++ If-else-if C++ Switch C++ Break C++ Continue C++ Goto C++ For loop C++ While loop C++ Do while loop

C++ Functions

C++ Call by Value C++ Call by Reference C++ Recursion Function C++ Inline function C++ Friend function

C++ Arrays

Single dimension array Two dimension array

C++ Strings

C++ Strings

C++ Inheritance

C++ Inheritance Single level Inheritance Multilevel Inheritance Multiple Inheritance Hierarchical Inheritance Hybrid Inheritance

C++ Polymorphism

C++ Polymorphism C++ Overloading C++ Overriding C++ Virtual Function

C++ Pointers

C++ Pointers C++ this pointer

C++ Exception Handling

C++ Exception Handling

C++ Constructors

C++ Constructors Default Constructor Parameterize Constructor Copy constructor Constructor Overloading Destructor

C++ File Handling

C++ File Handling C++ Writing to file C++ Reading file C++ Close file

Miscellaneous

C Vs C++ C++ Comments C++ Data Abstraction C++ Identifier C++ Memory Management C++ Storage Classes C++ Void Pointer C++ Array To Function C++ Expressions C++ Features C++ Interfaces C++ Encapsulation std::min in C++ External merge sort in C++ Remove duplicates from sorted array in C++ Precision of floating point numbers Using these functions floor(), ceil(), trunc(), round() and setprecision() in C++ C++ References C++ Friend Functions C++ Mutable keyword Unary Operators in C++ Initialize Array of objects with parameterized constructors in C++ Differences between #define & const in C/C++ C++ Program to Implement Shell Sort C++ Program to Implement Merge Sort Storage Classes in C Vector resize() in C++ Passing by Reference Vs. Passing by the pointer in C++ Free vs delete() in C++ goto statement in C and C++ C++ program to read string using cin.getline() C++ String Concatenation Heap Sort in C++ Swap numbers in C++ Input Iterators in C++ Fibonacci Series in C++ C ++ Program: Alphabet Triangle and Number Triangle C++ Program: Matrix Multiplication C++ Program to Print Fibonacci Triangle Stack in C++ Maps in C++ Queue in C++ C++ Bitset C++ Algorithms Priority Queue in C++ C++ Multimap C++ Deque Function Pointer in C++ Sizeof() Operators in C++ C++ array of Pointers free() Vs delete in C Timsort Implementation Using C++ CPP Templates C++ Aggregation C++ Enumeration C++ Math Functions C++ Object Class C++ Queue Initialize Vector in C++ Vector in C++ C++ STL Components Function overloading in C++ C++ Maximum Index Problem C++ find missing in the second array C++ Program to find the product array puzzle C++ Program To Find Largest Subarray With 0 Sum C++ Program To Move All Zeros To The End Of The Array C++ Program to find the element that occurs once C++ Program to find the largest number formed from an array Constructor Vs Destructor C++ Namespaces C++ OOPs Concept C++ Static C++ Structs C++ Try-Catch C++ User Defined Exceptions C++ Virtual Destructor C++ vs C# Malloc() and new in C++ Palindrome Number Program in C++ Snake Code in C++ Splitting a string in C++ Structure Vs Class in C++ Virtual Function Vs Pure Virtual Function C++ Bidirectional Iterators C++ Forward Iterators C++ Iterators C++ Output Iterators C++ Range-based For Loop Converting string into integer in C++ LCM Program in C++ Type conversion in C++ Add two numbers using the function in C++ Advantage and disadvantage friend function C++ Armstrong Number Program in C++ ATM machine program in C++ using functions Binary to Decimal in C++ Bit Manipulation in C++ C++ Constructor C++ Dijkstra Algorithm Using the Priority Queue C++ int into String C++ Signal Handling Decimal to Binary in C++ Decimal to Hexadecimal in C++ Decimal to Octal in C++ Factorial Program in C++ Function in C++ Hexadecimal to Decimal in C++ Octal to Decimal in C++ Reverse a Number in C++ Structure Vs Class in C++ C++ Forward Iterators C++ Output Iterators C++ Prime number program Char Array to String in C++ Constructor Overloading in C++ Default arguments in C++ Different Ways to Compare Strings in C++ Dynamic Binding in C++ Program to convert infix to postfix expression in C++ SET Data Structure in C++ Upcasting and Downcasting in C++ Reverse an Array in C++ Fast Input and Output in C++ Delete Operator in C++ Copy elision in C++ C++ Date and Time C++ Bitwise XOR Operator Array of sets in C++ Binary Operator Overloading in C++ Binary Search in C++ Implementing the sets without C++ STL containers Scope Resolution Operator in C++ Smart pointers in C++ Types of polymorphism in C++ Exception Handling in C++ vs Java Const Keyword in C++ Type Casting in C++ Static keyword in C++ vs Java Inheritance in C++ vs Java How to concatenate two strings in C++ Programs to Print Pyramid Patterns in C++ swap() function in C++ Structure of C++ Program Stringstream in C++ and its applications rand() and srand() in C / C++ C++ Ternary Operator C++ Scope of Variables While Loop Examples in C++ Star pattern in C++ using For Loops For Loop Examples in C++ Do-While Loop Examples in C++ Top 5 IDEs for C++ That You Should Try Once Assertions in C/C++ C++ Convert Int to String Continue in C++ While loop Diamond Pattern in C++ using For Loop How to Reverse a String in C++ using Do-While Loop How to Reverse a String in C++ using For Loop How to Reverse a String in C++ using While Loop Infinite loop in C++ Loops in C++ Returning Multiple Values from a Function using Tuple and Pair in C++ wcscpy(), wcslen(), wcscmp() Functions in C++

C++ Scope of Variables

In this tutorial, we will explore about the scope of variables in c++ programming language. And also, how it works in a program.

What is Scope?

The range of applications for something is generally referred to as its scope. The scope of a variable, as it relates to programming, is the area of the computer code that allows for access to, declaration of, and manipulation of the variable.

This implies that the name of a program element, such as a class, function, or variable, that is declared can only be "seen" and utilised in specific places inside our program. The term "scope" refers to the environment in which a name is visible. For instance, if a variable named m1 is declared inside a function, only that function body can see it. Its scope is local. Other variables with the same name may exist in our application, provided that they are in distinct scopes and do not violate the one definition rule. In this case, an error is not generated.

Scope also controls the creation and destruction of automatic non-static variables in program memory.

The rules that determine where a specific piece of code or piece of data would be known and accessible in a program are known as the scope rules of a language.

Different types of Scope:

  1. Global scope
  2. Local scope
  3. Namespace scope
  4. Class scope
  5. Statement scope
  6. Function scope
  7. Function parameter scope
  8. Enumeration scope
  9. Template parameter scope

However, the focus of this article will be on two different types of variable scope. Those are Local Variables, Global Variables.

1. Local Variables:

Local variables are those that are declared inside a function or block. Only statements included within that function or code block are permitted to use them. Outside of their own function, local variables are unknown. Here is an example of using local variables:

Code 1:

#include <iostream>
using namespace std;
 
int main () {
   // declaring local variables that can’t be accessed in outside of the block
   int m, n;
   int p;
 
   // initializing variables
   m = 20;
   n = 5;
   p = m * n;
 
   cout << p;
 
   return 0;
}

Code 2:

#include<iostream>
using namespace std;
 
void marksfunc()
{  
       // declaring local variables that can’t be accessed in outside of the function
    int marks = 95;   
}
 
int main()
{
    cout << "My annual marks is: " << marks;
     
    return 0;
}

Output:[Error]

13	39	C:\Users\X Y Z\Documents\Untitled1.cpp	[Error] 'marks' was not declared in this scope

Marks was not defined in this scope, according to the error message displayed by the software above. The variable marks was declared inside the function marksfunc(), making it specific to that function and invisible to the rest of the program.

Program Correction:

To fix the aforementioned error, we must simply show the value of the variable marks from the function marksfunc(). This is displayed in the code below:

Code:

#include<iostream>
using namespace std;


void marksfunc()
{
// declaring local variables that cant be accessed in outside of the function
	int marks = 95;
	cout <<marks;
}


int main()
{
	cout<<"My annual marks is: ";
	
	marksfunc();


	
	return 0;
}

Output:

My annual marks is: 95

2. Global Variables:

Global variables are typically defined on top of the program, outside of all the functions. The values of the global variables will remain constant over the course of your program.

Any function may access a global variable. In other words, once a global variable has been declared, it can be used throughout the entire program. The example utilizing both global and local variables is as follows:

Code:

#include<iostream>
using namespace std;
 
// declaring global variable
int global_var = 8;


//Inside a function, a global variable is accessed
void glob_display()
{
    cout << global_var << endl;
} 
 
// main function
int main()
{
    glob_display();
     
    //altering a global variable's value from the main function
    global_var = 16;
    glob_display();
}

Output:

8
16

The variable "global" in the program is declared at the beginning, outside of all the functions, making it a global variable that can be used anywhere in the program.

What if a function contains a local variable inside it with the same name as a global variable?

To further grasp the issue, take a look at the program below:

Code:

#include<iostream>
using namespace std;


// declaring global variable
int global_var = 12;


// main function
int main()
{
	//initializing local variable with the same name as global variable  
	
	int global_var = 7;
	cout << global_var << endl;
}

Have a look at the programme above. A local variable in main function declares a value of 7, but the global variable named "global_var" declares a value of 12. So what will happen when the main function prints the value that is saved in the variable called "global"? 7 or 12?

  • Usually, the compiler generates a compile time error when two variables with the same name are defined. However, the compiler permits it if the variables are specified in different scopes.
  • The compiler ensures that the local variable always has precedence over global variables when their names are same.

Output:

7

How can we access a local variable that shares the same name as a global variable?

We must utilize the scope resolution operator to resolve this issue. The program below demonstrates how to do this by use the scope resolution operator.

Code:

// C++ program to demonstrate access to a global variable


#include<iostream>
using namespace std;


// declaring global variable as var
int var = 6;


int main()
{
//  declaring local variable as var
int var = 13;


//Using the scope resolution operator " :: " , when a local variable with the same name exists
cout << "Value of global 'var' is " << ::var;


cout << "\nValue of local 'var' is " << var;
return 0;
}

Output:

Value of global 'var' is 6
Value of local 'var' is 13



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