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 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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++ Auto keyword in C++ C++ 11 vs C++ 14 vs C++ 17 C++ STL (Standard Template Library) Differences Between C Structures and C++ Structures Divide by Zero Exception in C++ Dynamic Constructor in C++ Dynamic Memory Allocation in C++ Find the Size of Array in C/C++ without using sizeof() function Floating Point Operations and Associativity in C, C++ and Java Hello World Program in C++ How to create a table in C++ How to Setup Environment for C++ Programming on Mac Implementation of a Falling Matrix in C++ Message Passing in C++ Pointer to Object in C++ Templates in C++ vs Generics in Java Ways to Copy a Vector in C++ What does Buffer Flush mean in C++ sort() function in C++ Structure Sorting (By Multiple Rules) in C++ Similarities between C++ and Java std::distance in C++ Array program in C++ C++ Tricks for Competitive Programming Desired Capabilities in Selenium Web Driver in C++ Socket Programming in C++ Template Specialization in C++ Classes and Objects in C++ Convex hull Algorithm in C++ DES in C++ C++ vardiac() function Difference between Two Sets in C++ Difference between Exit and Return Structured Binding in C++ Differences between Local and Global Variable Bitwise Operator vs Logical Operator Difference between OOP and POP in C++ Fork in C++ Functors in C++ How to call a void function in C++ How to create a directory or folder in C/C++ How to create a library in C++ How to create a stack in C++ How to create the Processes with Fork in C++ How to Handle Divide by Zero Exception in C++ Lambda Expression in C++ Pattern programs in C++ Roadmap to C++ Programming Substring in C++ Virtual base class in C++ Bits stdc++.h in C++ Top 14 Best Free C++ IDE (Editor & Compiler) for Windows in 2022 Bitmasking in C++ Auto Keyword in C++ Features of OOPS in C++ Hospital Management Project in C++ How to Declare Unordered Sets in C++ How to Sort an Array in C++ Include Guards in C++ Iostream in C++ Method overriding in C++ How to run program in turbo c++ How to Use Getline in C++ Leap Year Program in C++ Naming Convention in C++ New Operator in C++ Nullptr in C++ Object Slicing in C++ Principles of Object-Oriented Programming in C++ Processing strings using std string stream in C++ Pure Virtual Function in C++ With Example Program Random Number Generator in C++ Singleton Design Pattern in C++ Size_t Data Type in C++ Skyline Problem in C++ System() function in C++ Web Development in C++ Data Hiding in C++ Difference between exit() and _Exit() in C++ Hashing in C++ Object in C++ Sum of all Elements between k1’th and k2’th Smallest Elements Virtual class in C++ Vector Size in C++ Top best IDEs for C/C++ Developers in 2022 Tensorflow in C++ Sliding Window Technique in C++ Reverse String Word-Wise in C++ Returning a Function Pointer from a Function in C/C++ RTTI in C++ Pthreads or POSIX Threads in C++ Reserved Keywords in C++ Passing a Vector to a function in C++ 10 Best C and C++ Books for Beginners & Advanced Programmers Add two numbers represented by two arrays in C++ Array of Object in C++ C++ Program For FCFS Containership in C++ Counting Frequencies of Array Elements in C++ Decltype type Specifier in C++ Dynamic _Cast in C++ Difference between int main() and int main(void) in C/C++ Depth First Search Program to Traverse a Graph in C++ Features and Use Of Pointers in C/C++ Fread Function in C++ Programming Fscanf Function in The C++ Functions in C++ With Types and Examples Gmtime Function in C/C++ How is Multiset Implemented in C++ How to Build a Program in C++ How to Declare a 2d Array Dynamically in C++ inheritance Program in C++ int Max and int Min in C/C++ is It Fine to Write Void Main Or Main in C/C++ How to create a button in C++ abs() function in C++ Compile Time Polymorphism in C++ Division in C++ Factorial of a Number in C++ using while Loop Multiset in C++ 4 Pillars of OOPs Approach in C++ Backtracking Time Complexity in C++ C++ Global Variable C++ Pipe Tutorial Observer Design Pattern in C++ Private Inheritance in C++ Pthread in C++ Parameters SDL library in C++ with Examples Pointers in C++ Abstract Factory Design Pattern in C++ Ascending order in C++ How the value is passed in C++ Call by Pointer in C++ Constexpr in C++ Deadlock in C++ Design Patterns in C++ Factory Method for Designing Pattern in C++ How to calculate size of string in C++ Name Mangling and extern in C++ Preventing Object Copy in C++ Program that produces different results in C and C++ Quick Sort in C++ Single Handling in C++ Type difference of Character literals in C VS C++ Use of Inheritance in C++ User-defined literals in C++ Vector methods in C++ Void * in C and C++ Zombie and Orphan Process in C++ Isprint() in C++ List and Vector in C++ List iterators in C++ Merging Two Vectors in C++ Sleep function in C++ Stoi function in C++ String erase() in C++ String Trim in C++ When should we write own Assignment operator in C++ C++ tcp client server example C++ tcp server example Early Binding and Late Binding in C++ Factory Design Pattern in C++ Fisher-Yates shuffle algorithm in C++ For Auto in C++ Group anagrams in C++ How to convert binary string to int in C++ How to convert string to float in C++ How to remove space from string in C++ How to use pair in C++ How to use the string find() in C++ Dynamic Casting in C++ 2D Vector Initialization in C++ C++ GUI Visual Studio C++ IPC C++ Macro Function Example C++ Permutation Overloading Stream Insertion in C++ Overloading array Index operator in C++ Operators that cannot be overloaded in C++ Operator overloading in C++ isprint() function in c++ Is_trivial function in C++ Is assignment operator Inherited in C++ div() function in C++ Default Assignment Operator and References in C++ Copy Constructor vs Assignment Operator in C++ Conversion Operator in C++ Array sum in C++ STL C++ Define Macro C++ Design C++ Factory Pattern TCP Client Server Example in C++ Convert String to Uppercase in C++ exit() and _Exit() in C and C++ Initializer list in C++ Iterator invalidation in C++ Lower bound in C++ Modulus of Two float numbers or double number Pass by value in C++ Set insert function in C++ Std partition_point in C++ Unary Operator Overloading in C++ Using Default Arguments with Virtual Functions Virtual Functions and Runtime Polymorphism What is endl in C++ What is Unary Operator Overloading in C++ Which operators cannot be overloaded in C++ C++ Program to Divide the String Into N equal Parts Gray Code to Binary Code in C++ How to get the value of pi in C++ Multimap value_comp() function in C++ Vector of Vectors in C++ Naïve Bayes Algorithm in C++ Minimum Cost Path Problem in C++ 10 C++ Programming Tricks You Should Know btowc() function in C++ forward_list::cend() in C++ Unordered_multimap max_load_factor() function in C++ Cpp_int in c++ Dynamic Objects in C++ FLOCK() FUNCTION IN C++ Generate Random Double Numbers in C++ How to Assign Infinity to a Number in C++ Jump statements in C++ Multipath inheritance in C++ Out of Range Exception in C++ Size of Class in C++ Size of string in C++ std::binary_negate in c++ Thread_local in C++ Tokenizing a String in C++ Ancestors of a Node in Binary Search Tree C++ program for Double to String Conversion C++ Program to Demonstrate Use of Formatting Flags on Float Output Clamp in C++ K-Dimensional Tree in C++ Mutable Lambda in C++ Power Set in C++ Program to Find Sum of Geometric Progression Std::Back_inserter in C++ Strpbrk() function in C++ Size of int in C++ TYPES OF MANIPULATORS IN C++ Double colon in C++ How to sort vector in C++ How to use Setprecision in C++ How to write a Vector in C++ Insertion in Splay Tree in C++ Merge Sort Algorithm in C++ Printing a Character using ASCII value in C++ Regex in C++ Size of Data Types in C++ Sqrtf() function in C++ Static Casting in C++ Using Range in Switch Case in C++ wcstoimax() and wcstoumax() function in C++ What is float in C++ What is the Diamond Problem in C++ Best way to learn C++ ios setstate() function in C++ Nested Namespace in C++ Single Inheritance in C++ std::fixed, std::scientific, std::hexfloat, std::defaultfloat in C++ StringStream in C++ for Decimal to Hexadecimal and back The OFFSETOF() macro in C++ Difference between std::next and std::advance in C++ Hiding of all overloaded methods with same name in base class in C++ C++ program to concatenate two strings using operator overloading Difference between array::fill() and array::swap() in C++ Difference between Friend Function and Virtual Function in C++ Semaphores in C++ Seekg in C++ UDP server- client implementattion in C++ What is long long in C++ CSV file management using C++ Toggle bits of a number except first and last bits in C++ Trailing Return Type C++ 11 Binary search implementation in C++ Different Versions of C++ What is Cascading in C++ Background Colour in C++ BOOL DATATYPE IN C++ BIT VECTORS IN C++ Literals in C++ Application of pointer in C++ Index with minimum sum of prefix and suffix sums in an array in C++ Maximum sum Bi-tonic sub-sequence in C++ std::optional in C++ C/C++ program for triangular matchstick number COUT COMMAND IN C++ LANGUAGE Adjacency matrix program in C++ language Difference between Null String and Empty String in C++ Character data type in c++ Constructors in Inheritance C++ Comma Operator Overloading in C++ Structure and Class in C++ Template Definition in C++ Tree Data Structure in C++ Typename in C++ C++ program to implement the bin packing algorithm How to merge multiple std::sets into a single std::set in C++? Stack Clear C++ C++ Friend Class Seekg in C++ Semaphores in C++ C++ Exceptions Difference Between C and C++ Double-linked list program in C++ Color Code in C++ CRC Program in C++ Anti-Clockwise spiral traversal of a binary tree in C++ Advantages of OOP in C++ Cryptarithmetic Puzzle in C++ Angular sweep algorithm in C++

Const Keyword in C++

The const programming language keyword will be covered in this section. The constant value that cannot change during program execution is defined using the const keywords. It implies that once a variable is designated as a constant in a program, its value cannot be altered.

  • A function can be invoked on any kind of object, including const and non-const objects, when it is defined as const.
  • An object must be initialized at the moment of declaration whenever it is specified as const. However, only constructors make it feasible to initialize an object when declaring.

Const keywords with various parameters:

  • Using Const variable
  • Using pointers, use const
  • Using variables, use a const pointer
  • When using function arguments use const.
  • Const with member functions of classes
  • Using class data members, use const
  • Using class objects, use const.

Constant Variable

It is a const variable that is used to define variables with constant values during program execution. Additionally, it throws an error if we attempt to change the value.

const data_type variable_name ;   //syntax

Example1: Let's write a program to show how to utilize the C++ programming language's const keyword.

#include < iostream >  
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >
#include < conio.h >  
using namespace std ;  
int main ( )  
{  
// declare the value of the const  
const int num = 25 ;  
num = num + 10 ;  
return 0 ;  
}  

OUTPUT:

Because we increase the allocated value of the num 25 by 10, the compile-time error is visible.

Example2: Let's write a straightforward program to show how to utilize the C++ programming language's const keyword.

/* create a program to use the const keyword with different data types in the C++. */  
#include < iostream >  
#include < conio.h >
#include <bits/stdc++.h>
#include <stdio>
#Include <stdlib>  
using namespace std;  
int main ( )  
{  
// declare variables  
const int x = 20 ;  
const int y = 25 ;  
int z ;  
// add the value of x and y  
z = x + y ;  
cout << " The sum of the x and y is: " << z << endl ;  
return 0 ;  
}  

OUTPUT:

The sum of the x and y is: 42
.............................
Process executed in 2.11 seconds
Press any key to continue.

Explanation

The const variables x and y were defined and initialized in the program above. Then, display the total by storing the output of two const variables in the 'z' variable.

NOTE: In order to avoid a compile-time error, we must assign the values of the declared variables simultaneously with the definition of the const variable in C++ programming.

Constant Pointer

We must use the const keyword before the pointer's name in order to build a const pointer. The const pointer cannot have its address changed after it is initialised, therefore once it is initialized as a const pointer, it will always point to the same location.

Example3: A program that uses the keyword const to illustrate the constant pointer

Let's look at an example of how to utilize the C++ programming language's const keyword with a constant pointer.

#include < iostream >  
#include < bits/stdc++.h >
#include < stdlib >
#include < stdio >
#include < conio.h >
using namespace std ;  
int main ( )  
{  
// declaration of the integer variables  
int x = 10 , y = 20 ;  
  
// use const keyword to make constant pointer  
int * const ptr = & x ; //  const integer ptr variable point address to the variable x  
  
// ptr = & y ; // now ptr cannot changed their address  
* ptr = 15 ; // ptr can only change the value  
cout << " The value of x: " << x << endl ;  
cout << " The value of ptr: " << * ptr << endl ;  
return 0 ;  
} 

OUTPUT:

The value of x : 15
The value of ptr : 15
..............................
Process executed in 1.22 seconds
Press any key to continue.

Explanation

The pointer ptr in the program above can modify the value of x but cannot change the address of the int variable 'x' or the ptr variable once they have been created.

Pointer to constant variable

It indicates that the pointer corresponds to a constant variable whose value cannot change.

const int * x ;   //declaration syntax

Here, the variable x is a pointer to a const integer type variable. A pointer to the constant variable can alternatively be declared as

char const * y ; //declaration syntax

In this instance, y is a reference to a variable of type char that is const.

Example4: A program that points to a constant variable and uses the const keyword

#include < iostream >
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >  
#include < conio.h >
using namespace std ;  
int main ( )  
{  
// declare integer variable  
int x = 7 , y = 10 ;  
  
const int * ptr = & x ; // here x become constant variable  
cout << " \n The initial value of ptr: " << * ptr ;  
cout << " \n The value of x: " << x ;  
  
// * ptr = 15 ; It is invalid; we cannot directly assign a value to the ptr variable  
ptr = & y ; //  here ptr variable pointing to the non const address 'y'  
  
cout << " \n The value of y: " << y ;  
cout << " \n The value of ptr:" << * ptr ;   
return 0 ;  
}  

OUTPUT:

The initial value of ptr: 7
The value of x: 7
The value of y: 10
The value of ptr: 10
...........................
Process execute in 2.22 seconds
Press any key to continue.

Explanation

In the program above, the const int ( x ) variable is pointed to by pointer ptr, and its value is immutable.

Arguments for constant functions

Using the term const, we may specify the function parameters as constant arguments. Additionally, if a function argument's value is marked const, it is not possible to change it.

return_type fun_name ( const int x )  //syntax
{  
}  

Return type in the aforementioned syntax indicates whether or not the function will return a value. Fun name ( ) has a const parameter, which means that once it is defined in the program, its value cannot be altered.

Example5: Let's look at an example of how to utilize the C++ programming language's const keyword with function parameters.

#include < iostream >
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >  
#include < conio.h >
using namespace std ;  
// create an integer Test ( ) function contains an argument num  
int Test ( const int num )  
{  
// if we change the value of the const argument, it thwrows an error.  
// num = num + 10 ;  
cout << " The value of num: " << num << endl ;  
return 0 ;  
}  
int main ( )  
{  
// call function  
Test ( 5 ) ;  
}  

OUTPUT:

The value of num: 5
...................
Process executed in 1.11 seconds
Press any key to continue.

Explanation

The num parameter in the program above is a constant, thus we are unable to change its value. The compile-time error is returned if the value of the num variable is modified.

Another Example:

// C++ program to demonstrate the
// constant function
#include < iostream >
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >  
#include < conio.h >
using namespace std ;  
// Class Test
class Test {
	int value ; 
public :
	// Constructor
	Test ( int v = 0 )
	{
		value = v ;
	}
	// We get compiler error if we
	// add a line like "value = 100;"
	// in this function.
	int getValue () const
	{
		return value;
	}
	// a nonconst function trying to modify value
	void setValue (int val) {
		value = val;
	}
 }; 
// Driver Code
int main ()
{
	// Object of the class T
	Test t (20); 
	// non-const object invoking const function, no error
	cout << t.getValue() << endl ; 
	// const object
	const Test t_const(10); 
	// const object invoking const function, no error
	cout << t_const.getValue() << endl; 
	// const object invoking non-const function, CTe
	// t_const . setValue(15); 
	// non-const object invoking non-const function, no error
	t . setValue(12); 
	cout << t . getValue ( ) << endl ; 
	return 0 ;
}

OUTPUT:

20

Explanation

In the above program if we try calling the non constant function from a constant object then it will give us an error stating that “passing const test as this argument discard qualifier [ -fpermissive ]”

Const member of class function

  • A constant member function of a class is called a const if it never modifies any class data members or calls any non-const functions.
  • Additionally called the read-only function.
  • By using the const keyword after the member function's name, we may turn a class member function into a constant one.
return_type mem_fun ( ) //syntax
{
}

mem_fun ( ), which is a member function of a class in the syntax above, is made constant by the use of the const keyword after its name.

Example6: A program to utilize the class member function and the const keyword

Let's look at an illustration of how to define the const keyword using a class member function.

class ABC  
{  
// define the access specifier  
public :  
  
// declare int variables  
int A ;  
// declare member function as constant using const keyword  
void fun ( ) const  
{  
 A = 0 ; // it shows compile time error  
}  
} ;  
  
int main ( )  
{  
    ABC obj ;  
    obj . fun ( ) ;  
    return 0 ;  
}  

OUTPUT:

Because we are attempting to give a value to the fun ( ) function's data member 'x', which returns an error, which is a const member function of class ABC, the aforementioned code generates a compilation error.

Constant Data Class Member

Data members are similar to variables defined inside of classes, but once initialized, they remain immutable not even in constructors or destructors. The const keyword is used before the class's data type to initialize the constant data member. Const data members cannot have values assigned to them at declaration, however function Object () { [native code] } values may be assigned.

Example7: A program that uses the const keyword with the class's Data members

/* create a program to demonstrate the data member using the const keyword in C++. */   
#include < iostream >
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >  
#include < conio.h >
using namespace std ;  
// create a class ABC  
class ABC  
{  
public :  
 // use const keyword to declare const data member  
const int A ;  
// create class constructor  
ABC ( int y ) : A ( y )  
{  
cout << " The value of y : " << y << endl ;  
}  
} ;  
int main ( )  
{  
ABC obj ( 10 ) ; // here ' obj ' is the object of class ABC  
cout << " The value of constant data member ' A ' is : " << obj . A << endl ;  
// obj . A = 5 ; // it shows an error.  
// cout << obj . A << endl ;  
return 0 ;  
}  

OUTPUT:

The value of y: 10
The value of constant data member 'A' is: 10
.........................................................................
Process executed in 1.22 seconds
Press any key to continue.

Explanation

In the program above, the object of the ABC class, named obj, calls the ABC function Object ( ) { [ native code ] } to display the value of y. Next, it publishes the value of the const data member 'A,' which is 10 in the program. However, because A's value is fixed and cannot be modified, a compile-time error is displayed when "obj . A" assigns a new value to the "A" data member.

Constant Objects

The value of data members can never change while an object is being created using the const keyword in a program. The read-only objects are also referred to as const objects.

const class_name obj_name ; //syntax

In the syntax above, the term const is used before the name of the class object to designate that it is a constant object.

Example8: Let's write a program in the C++ programming language that utilises constant objects.

#include < iostream >
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >  
#include < conio.h >
using namespace std ;  
class ABC  
{  
public :  
// define data member  
int A ;  
// create constructor of the class ABC  
ABC ( )  
{  
A = 10 ; // define a value to A  
}  
} ;  
int main ( )  
{  
// declare a constant object  
const ABC obj ;  
cout << " The value of A : " << obj . A << endl ;  
// obj . A = 20 ; // It returns a compile time error  
return 0 ;  
}  

OUTPUT:

The value of A: 10
..............................
Process executed in 2.22 seconds
Press any key to continue.

Explanation

In the program above, if we set the value of A to 10, the compiler outputs "The value of A: 10," and if we set the value of A to 20, the class object produces a compile-time error.

A Program that uses the const keyword to calculate the area of a circle

Example9: Let's look at a C++ programming example that uses the const keyword to print a circle's area.

#include < iostream >
#include < bits/stdc++.h >
#include < stdio >
#include < stdlib >  
#include < conio.h >
using namespace std ;  
int main ( )  
{  
// declare variables  
int r ;  
const double PI = 3 . 14 ;  
double result ;  
cout << " Input the radius of a circle : " << endl ;  
cin >> r ;  
result = PI * r * r ;  
cout << " The area of a circle is : " << result ;  
}  

OUTPUT:

Input the radius of a circle: 
5
The area of a circle is: 78.5
…………………………………………
Process executed in 2.22 seconds
Press any key to continue.

Explanation

In the above example of a program in C++, we have shown how to calculate the area of a circle using constant variable.