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C++ Programming Code Examples

C++ > Games Code Examples

To solve josephus problem using circular queue and templates

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/* To solve josephus problem using circular queue and templates */ //////////////////Header file #include<iostream.h> template <class T> class ex { private: struct node { T data; struct node *next; }; struct node *head,*front,*rear; public: ex() { head=new node; head->next=NULL; front=rear=head; } void enqueue(T x); T dequeue(); void print(); void move_next(); }; //////////////////Implementation file #include "ex.h" template <class T> void ex<T>::enqueue(T x) { node *p; p=new node; p->data=x; if(head->next==NULL) { front=rear=p; head->next=p; p->next=p; } else { rear->next=p; p->next=front; rear=rear->next; } } template<class T> T ex<T>::dequeue() { node *t; T x; t=front; x=t->data; front=front->next; rear->next=front; delete(t); return x; } template<class T> void ex<T>::print() { node *p=front; do { cout<<p->data<<endl; p=p->next; }while(p!=rear->next); } template<class T> void ex<T>::move_next() { front=front->next; rear=rear->next; } /////////////////Application file #include "ex.cpp" void main() { ex<int> e; int m,n,i,d; cout<<"Enter the number of people "; cin>>n; cout<<"Enter the number of passes "; cin>>m; for(i=1;i<=n;i++) e.enqueue(i); cout<<"The players are "; e.print(); cout<<"Eliminated in order "; while(n>1) { for(i=1;i<=m;i++) e.move_next(); d=e.dequeue(); cout<<d<<endl; n--; } d=e.dequeue(); cout<<"Winning player: "<<d<<endl; }
If Else Statement in C++
In computer programming, we use the if statement to run a block code only when a certain condition is met. An if statement can be followed by an optional else statement, which executes when the boolean expression is false. There are three forms of if...else statements in C++: • if statement, • if...else statement, • if...else if...else statement,
Syntax for If Statement in C++
if (condition) { // body of if statement }
The if statement evaluates the condition inside the parentheses ( ). If the condition evaluates to true, the code inside the body of if is executed. If the condition evaluates to false, the code inside the body of if is skipped.
Syntax for If...Else Statement
if (condition) { // block of code if condition is true } else { // block of code if condition is false }
The if..else statement evaluates the condition inside the parenthesis. If the condition evaluates true, the code inside the body of if is executed, the code inside the body of else is skipped from execution. If the condition evaluates false, the code inside the body of else is executed, the code inside the body of if is skipped from execution. The if...else statement is used to execute a block of code among two alternatives. However, if we need to make a choice between more than two alternatives, we use the if...else if...else statement.
Syntax for If...Else...Else If Statement in C++
if (condition1) { // code block 1 } else if (condition2){ // code block 2 } else { // code block 3 }
• If condition1 evaluates to true, the code block 1 is executed. • If condition1 evaluates to false, then condition2 is evaluated. • If condition2 is true, the code block 2 is executed. • If condition2 is false, the code block 3 is executed. There can be more than one else if statement but only one if and else statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax for If Else If Ladder in C++
if (condition) statement 1; else if (condition) statement 2; . . else statement;
Working of the if-else-if ladder: 1. Control falls into the if block. 2. The flow jumps to Condition 1. 3. Condition is tested. If Condition yields true, goto Step 4. If Condition yields false, goto Step 5. 4. The present block is executed. Goto Step 7. 5. The flow jumps to Condition 2. If Condition yields true, goto step 4. If Condition yields false, goto Step 6. 6. The flow jumps to Condition 3. If Condition yields true, goto step 4. If Condition yields false, execute else block. Goto Step 7. 7. Exits the if-else-if ladder. • The if else ladder statement in C++ programming language is used to check set of conditions in sequence. • This is useful when we want to selectively executes one code block(out of many) based on certain conditions. • It allows us to check for multiple condition expressions and execute different code blocks for more than two conditions. • A condition expression is tested only when all previous if conditions in if-else ladder is false. • If any of the conditional expression evaluates to true, then it will execute the corresponding code block and exits whole if-else ladder.
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/* If Else Statement in C++ Language */ #include <iostream> using namespace std; int main () { // local variable declaration: int a = 100; // check the boolean condition if( a < 20 ) { // if condition is true then print the following cout << "a is less than 20;" << endl; } else { // if condition is false then print the following cout << "a is not less than 20;" << endl; } cout << "value of a is : " << a << endl; return 0; }
Standard Input Stream (cin) in C++
The cin object is used to accept input from the standard input device i.e. keyboard. It is defined in the iostream header file. C++ cin statement is the instance of the class istream and is used to read input from the standard input device which is usually a keyboard. The extraction operator(>>) is used along with the object cin for reading inputs. The extraction operator extracts the data from the object cin which is entered using the keyboard.
Syntax for Standard Input Stream (cin) in C++
cin >> var_name;
>>
is the extraction operator.
var_name
is usually a variable, but can also be an element of containers like arrays, vectors, lists, etc. The "c" in cin refers to "character" and "in" means "input". Hence cin means "character input". The cin object is used along with the extraction operator >> in order to receive a stream of characters. The >> operator can also be used more than once in the same statement to accept multiple inputs. The cin object can also be used with other member functions such as getline(), read(), etc. Some of the commonly used member functions are: • cin.get(char &ch): Reads an input character and stores it in ch. • cin.getline(char *buffer, int length): Reads a stream of characters into the string buffer, It stops when: it has read length-1 characters or when it finds an end-of-line character '\n' or the end of the file eof. • cin.read(char *buffer, int n): Reads n bytes (or until the end of the file) from the stream into the buffer. • cin.ignore(int n): Ignores the next n characters from the input stream. • cin.eof(): Returns a non-zero value if the end of file (eof) is reached. The prototype of cin as defined in the iostream header file is: extern istream cin; The cin object in C++ is an object of class istream. It is associated with the standard C input stream stdin. The cin object is ensured to be initialized during or before the first time an object of type ios_base::Init is constructed. After the cin object is constructed, cin.tie() returns &cout. This means that any formatted input operation on cin forces a call to cout.flush() if any characters are pending for output.
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/* Standard Input Stream (cin) in C++ language */ // cin with Member Functions #include <iostream> using namespace std; int main() { char name[20], address[20]; cout << "Name: "; // use cin with getline() cin.getline(name, 20); cout << "Address: "; cin.getline(address, 20); cout << endl << "You entered " << endl; cout << "Name = " << name << endl; cout << "Address = " << address; return 0; }
#include Directive in C++
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
Syntax for #include Directive in C++
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories. Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor. • In #include directive, comments are not recognized. So in case of #include <a//b>, a//b is treated as filename. • In #include directive, backslash is considered as normal text not escape sequence. So in case of #include <a\nb>, a\nb is treated as filename. • You can use only comment after filename otherwise it will give error.
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/* using #include directive in C language */ #include <stdio.h> int main() { /* * C standard library printf function * defined in the stdio.h header file */ printf("I love you Clementine"); printf("I love you so much"); printf("HappyCodings"); return 0; }
Function Templates in C++
A C++ template is a powerful feature added to C++. It allows you to define the generic classes and generic functions and thus provides support for generic programming. Generic programming is a technique where generic types are used as parameters in algorithms so that they can work for a variety of data types. We can define a template for a function. For example, if we have an add() function, we can create versions of the add function for adding the int, float or double type values.
Syntax for Function Templates in C++
template < class Ttype> ret_type func_name(parameter_list) { // body of function. }
Ttype
a placeholder name
class
specify a generic type Where Ttype: It is a placeholder name for a data type used by the function. It is used within the function definition. It is only a placeholder that the compiler will automatically replace this placeholder with the actual data type. class: A class keyword is used to specify a generic type in a template declaration. • Generic functions use the concept of a function template. Generic functions define a set of operations that can be applied to the various types of data. • The type of the data that the function will operate on depends on the type of the data passed as a parameter. • For example, Quick sorting algorithm is implemented using a generic function, it can be implemented to an array of integers or array of floats. • A Generic function is created by using the keyword template. The template defines what function will do. Function templates with multiple parameters: We can use more than one generic type in the template function by using the comma to separate the list.
template<class T1, class T2,.....> return_type function_name (arguments of type T1, T2....) { // body of function. }
Overloading a function template: We can overload the generic function means that the overloaded template functions can differ in the parameter list. Generic functions perform the same operation for all the versions of a function except the data type differs.
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/* function templates in C++ language */ /* adding two numbers using function templates */ #include <iostream> using namespace std; template <typename T> T add(T num1, T num2) { return (num1 + num2); } int main() { int result1; double result2; // calling with int parameters result1 = add<int>(2, 3); cout << "2 + 3 = " << result1 << endl; // calling with double parameters result2 = add<double>(2.2, 3.3); cout << "2.2 + 3.3 = " << result2 << endl; return 0; }
Classes and Objects in C++ Language
The main purpose of C++ programming is to add object orientation to the C programming language and classes are the central feature of C++ that supports object-oriented programming and are often called user-defined types. A class is used to specify the form of an object and it combines data representation and methods for manipulating that data into one neat package. The data and functions within a class are called members of the class.
C++ Class Definitions
When you define a class, you define a blueprint for a data type. This doesn't actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object. A class definition starts with the keyword class followed by the class name; and the class body, enclosed by a pair of curly braces. A class definition must be followed either by a semicolon or a list of declarations. For example, we defined the Box data type using the keyword class as follows:
class Box { public: double length; // Length of a box double breadth; // Breadth of a box double height; // Height of a box };
The keyword public determines the access attributes of the members of the class that follows it. A public member can be accessed from outside the class anywhere within the scope of the class object. You can also specify the members of a class as private or protected which we will discuss in a sub-section.
Define C++ Objects
A class provides the blueprints for objects, so basically an object is created from a class. We declare objects of a class with exactly the same sort of declaration that we declare variables of basic types. Following statements declare two objects of class Box:
Box Box1; // Declare Box1 of type Box Box Box2; // Declare Box2 of type Box
Both of the objects Box1 and Box2 will have their own copy of data members.
Accessing the Data Members
The public data members of objects of a class can be accessed using the direct member access operator (.). It is important to note that private and protected members can not be accessed directly using direct member access operator (.).
Classes and Objects in Detail
There are further interesting concepts related to C++ Classes and Objects which we will discuss in various sub-sections listed below: • Class Member Functions: A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. • Class Access Modifiers: A class member can be defined as public, private or protected. By default members would be assumed as private. • Constructor & Destructor: A class constructor is a special function in a class that is called when a new object of the class is created. A destructor is also a special function which is called when created object is deleted. • Copy Constructor: The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously. • Friend Functions: A friend function is permitted full access to private and protected members of a class. • Inline Functions: With an inline function, the compiler tries to expand the code in the body of the function in place of a call to the function. • this Pointer: Every object has a special pointer this which points to the object itself. • Pointer to C++ Classes: A pointer to a class is done exactly the same way a pointer to a structure is. In fact a class is really just a structure with functions in it. • Static Members of a Class: Both data members and function members of a class can be declared as static.
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/* using public and private in C++ Class */ // Program to illustrate the working of // public and private in C++ Class #include <iostream> using namespace std; class Room { private: double length; double breadth; double height; public: // function to initialize private variables void initData(double len, double brth, double hgt) { length = len; breadth = brth; height = hgt; } double calculateArea() { return length * breadth; } double calculateVolume() { return length * breadth * height; } }; int main() { // create object of Room class Room room1; // pass the values of private variables as arguments room1.initData(42.5, 30.8, 19.2); cout << "Area of Room = " << room1.calculateArea() << endl; cout << "Volume of Room = " << room1.calculateVolume() << endl; return 0; }
Standard end line (endl) in C++
A predefined object of the class called iostream class is used to insert the new line characters while flushing the stream is called endl in C++. This endl is similar to \n which performs the functionality of inserting new line characters but it does not flush the stream whereas endl does the job of inserting the new line characters while flushing the stream. Hence the statement cout<<endl; will be equal to the statement cout<< '\n' << flush; meaning the new line character used along with flush explicitly becomes equivalent to the endl statement in C++.
Syntax for end line (endl) in C++
cout<< statement to be executed <<endl;
Whenever the program is writing the output data to the stream, all the data will not be written to the terminal at once. Instead, it will be written to the buffer until enough data is collected in the buffer to output to the terminal. But if are using flush in our program, the entire output data will be flushed to the terminal directly without storing anything in the buffer. Whenever there is a need to insert the new line character to display the output in the next line while flushing the stream, we can make use of endl in C++. Whenever there is a need to insert the new line character to display the output in the next line, we can make use of endl in '\n' character but it does not do the job of flushing the stream. So if we want to insert a new line character along with flushing the stream, we make use of endl in C++. Whenever the program is writing the output data to the stream, all the data will not be written to the terminal at once. Instead, it will be written to the buffer until enough data is collected in the buffer to output to the terminal. • It is a manipulator. • It doesn't occupy any memory. • It is a keyword and would not specify any meaning when stored in a string. • We cannot write 'endl' in between double quotations. • It is only supported by C++. • It keeps flushing the queue in the output buffer throughout the process.
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/* Standard end line (endl) in C++ language */ //The header file iostream is imported to enable us to use cout in the program #include <iostream> //a namespace called std is defined using namespace std; //main method is called int main( ) { //cout is used to output the statement cout<< "Welcome to "; //cout is used to output the statement along with endl to start the next statement in the new line and flush the output stream cout<< "C#"<<endl; //cout is used to output the statement along with endl to start the next statement in the new line and flush the output stream cout<< "Learning is fun"<<endl; }
Memory Management new Operator in C++
Allocate storage space. Default allocation functions (single-object form). A new operator is used to create the object while a delete operator is used to delete the object. When the object is created by using the new operator, then the object will exist until we explicitly use the delete operator to delete the object. Therefore, we can say that the lifetime of the object is not related to the block structure of the program.
Syntax for new Operator in C++
#include <new> //throwing (1) void* operator new (std::size_t size); //nothrow (2) void* operator new (std::size_t size, const std::nothrow_t& nothrow_value) noexcept; //placement (3) void* operator new (std::size_t size, void* ptr) noexcept;
size
Size in bytes of the requested memory block. This is the size of the type specifier in the new-expression when called automatically by such an expression. If this argument is zero, the function still returns a distinct non-null pointer on success (although dereferencing this pointer leads to undefined behavior). size_t is an integral type.
nothrow_value
The constant nothrow. This parameter is only used to distinguish it from the first version with an overloaded version. When the nothrow constant is passed as second parameter to operator new, operator new returns a null-pointer on failure instead of throwing a bad_alloc exception. nothrow_t is the type of constant nothrow.
ptr
A pointer to an already-allocated memory block of the proper size. If called by a new-expression, the object is initialized (or constructed) at this location. For the first and second versions, function returns a pointer to the newly allocated storage space. For the third version, ptr is returned. • (1) throwing allocation: Allocates size bytes of storage, suitably aligned to represent any object of that size, and returns a non-null pointer to the first byte of this block. On failure, it throws a bad_alloc exception. • (2) nothrow allocation: Same as above (1), except that on failure it returns a null pointer instead of throwing an exception. The default definition allocates memory by calling the the first version: ::operator new (size). If replaced, both the first and second versions shall return pointers with identical properties. • (3) placement: Simply returns ptr (no storage is allocated). Notice though that, if the function is called by a new-expression, the proper initialization will be performed (for class objects, this includes calling its default constructor). The default allocation and deallocation functions are special components of the standard library; They have the following unique properties: • Global: All three versions of operator new are declared in the global namespace, not within the std namespace. • Implicit: The allocating versions ((1) and (2)) are implicitly declared in every translation unit of a C++ program, no matter whether header <new> is included or not. • Replaceable: The allocating versions ((1) and (2)) are also replaceable: A program may provide its own definition that replaces the one provided by default to produce the result described above, or can overload it for specific types. If set_new_handler has been used to define a new_handler function, this new-handler function is called by the default definitions of the allocating versions ((1) and (2)) if they fail to allocate the requested storage. operator new can be called explicitly as a regular function, but in C++, new is an operator with a very specific behavior: An expression with the new operator, first calls function operator new (i.e., this function) with the size of its type specifier as first argument, and if this is successful, it then automatically initializes or constructs the object (if needed). Finally, the expression evaluates as a pointer to the appropriate type.
Data races
Modifies the storage referenced by the returned value. Calls to allocation and deallocation functions that reuse the same unit of storage shall occur in a single total order where each deallocation happens entirely before the next allocation. This shall also apply to the observable behavior of custom replacements for this function.
Exception safety
The first version (1) throws bad_alloc if it fails to allocate storage. Otherwise, it throws no exceptions (no-throw guarantee).
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/* C++ allows us to allocate the memory of a variable or an array in run time. This is known as dynamic memory allocation. The new operator denotes a request for memory allocation on the Free Store. If sufficient memory is available, new operator initializes the memory and returns the address of the newly allocated and initialized memory to the pointer variable. */ /* Allocate storage space by operator new */ // C++ program code example to illustrate dynamic allocation and deallocation of memory using new and delete #include <iostream> using namespace std; int main () { // Pointer initialization to null int* p = NULL; // Request memory for the variable // using new operator p = new(nothrow) int; if (!p) cout << "allocation of memory failed\n"; else { // Store value at allocated address *p = 29; cout << "Value of p: " << *p << endl; } // Request block of memory // using new operator float *r = new float(75.25); cout << "Value of r: " << *r << endl; // Request block of memory of size n int n = 5; int *q = new(nothrow) int[n]; if (!q) cout << "allocation of memory failed\n"; else { for (int i = 0; i < n; i++) q[i] = i+1; cout << "Value store in block of memory: "; for (int i = 0; i < n; i++) cout << q[i] << " "; } // freed the allocated memory delete p; delete r; // freed the block of allocated memory delete[] q; return 0; }
Standard Output Stream (cout) in C++
The cout is a predefined object of ostream class. It is connected with the standard output device, which is usually a display screen. The cout is used in conjunction with stream insertion operator (<<) to display the output on a console. On most program environments, the standard output by default is the screen, and the C++ stream object defined to access it is cout.
Syntax for cout in C++
cout << var_name; //or cout << "Some String";
The syntax of the cout object in C++: cout << var_name; Or cout << "Some String";
<<
is the insertion operator
var_name
is usually a variable, but can also be an array element or elements of containers like vectors, lists, maps, etc. The "c" in cout refers to "character" and "out" means "output". Hence cout means "character output". The cout object is used along with the insertion operator << in order to display a stream of characters. The << operator can be used more than once with a combination of variables, strings, and manipulators. cout is used for displaying data on the screen. The operator << called as insertion operator or put to operator. The Insertion operator can be overloaded. Insertion operator is similar to the printf() operation in C. cout is the object of ostream class. Data flow direction is from variable to output device. Multiple outputs can be displayed using cout.
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/* standard output stream (cout) in C++ language */ #include <iostream> using namespace std; int main() { string str = "Do not interrupt me"; char ch = 'm'; // use cout with write() cout.write(str,6); cout << endl; // use cout with put() cout.put(ch); return 0; }
Nested Loop Statement in C++
C supports nesting of loops in C. Nesting of loops is the feature in C that allows the looping of statements inside another loop. Any number of loops can be defined inside another loop, i.e., there is no restriction for defining any number of loops. The nesting level can be defined at n times. You can define any type of loop inside another loop; for example, you can define 'while' loop inside a 'for' loop. A loop inside another loop is called a nested loop. The depth of nested loop depends on the complexity of a problem. We can have any number of nested loops as required. Consider a nested loop where the outer loop runs n times and consists of another loop inside it. The inner loop runs m times. Then, the total number of times the inner loop runs during the program execution is n*m.
Syntax for Nested Loop Statement in C++
Outer_loop { Inner_loop { // inner loop statements. } // outer loop statements. }
Outer_loop and Inner_loop are the valid loops that can be a 'for' loop, 'while' loop or 'do-while' loop.
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/* nested loop statement in C++ language */ // C++ program that uses nested for loop to print a 2D matrix #include <bits/stdc++.h> using namespace std; #define ROW 3 #define COL 3 // Driver program int main() { int i, j; // Declare the matrix int matrix[ROW][COL] = { { 4, 8, 12 }, { 16, 20, 24 }, { 28, 32, 36 } }; cout << "Given matrix is \n"; // Print the matrix using nested loops for (i = 0; i < ROW; i++) { for (j = 0; j < COL; j++) cout << matrix[i][j]; cout << "\n"; } return 0; }
Structures in C++ Language
In C++, classes and structs are blueprints that are used to create the instance of a class. Structs are used for lightweight objects such as Rectangle, color, Point, etc. Unlike class, structs in C++ are value type than reference type. It is useful if you have data that is not intended to be modified after creation of struct. C++ Structure is a collection of different data types. It is similar to the class that holds different types of data.
Syntax for Structures in C++
struct structureName{ member1; member2; member3; . . . memberN; };
A structure is declared by preceding the struct keyword followed by the identifier(structure name). Inside the curly braces, we can declare the member variables of different types. Consider the following situation:
struct Teacher { char name[20]; int id; int age; }
In the above case, Teacher is a structure contains three variables name, id, and age. When the structure is declared, no memory is allocated. When the variable of a structure is created, then the memory is allocated. Let's understand this scenario. Structures in C++ can contain two types of members: • Data Member: These members are normal C++ variables. We can create a structure with variables of different data types in C++. • Member Functions: These members are normal C++ functions. Along with variables, we can also include functions inside a structure declaration. Structure variable can be defined as: Teacher s; Here, s is a structure variable of type Teacher. When the structure variable is created, the memory will be allocated. Teacher structure contains one char variable and two integer variable. Therefore, the memory for one char variable is 1 byte and two ints will be 2*4 = 8. The total memory occupied by the s variable is 9 byte. The variable of the structure can be accessed by simply using the instance of the structure followed by the dot (.) operator and then the field of the structure.
s.id = 4;
We are accessing the id field of the structure Teacher by using the dot(.) operator and assigns the value 4 to the id field. In C++, the struct keyword is optional before in declaration of a variable. In C, it is mandatory.
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/* Structure is a collection of variables of different data types under a single name. It is similar to a class in that, both holds a collecion of data of different data types. */ #include <iostream> using namespace std; struct Person { char name[50]; int age; float salary; }; int main() { Person p1; cout << "Enter Full name: "; cin.get(p1.name, 50); cout << "Enter age: "; cin >> p1.age; cout << "Enter salary: "; cin >> p1.salary; cout << "\nDisplaying Information." << endl; cout << "Name: " << p1.name << endl; cout <<"Age: " << p1.age << endl; cout << "Salary: " << p1.salary; return 0; }
main() Function in C++
A program shall contain a global function named main, which is the designated start of the program in hosted environment. main() function is the entry point of any C++ program. It is the point at which execution of program is started. When a C++ program is executed, the execution control goes directly to the main() function. Every C++ program have a main() function.
Syntax for main() Function in C++
void main() { ............ ............ }
void
void is a keyword in C++ language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value.
main
main is a name of function which is predefined function in C++ library. In place of void we can also use int return type of main() function, at that time main() return integer type value. 1) It cannot be used anywhere in the program a) in particular, it cannot be called recursively b) its address cannot be taken 2) It cannot be predefined and cannot be overloaded: effectively, the name main in the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace). 3) It cannot be defined as deleted or (since C++11) declared with C language linkage, constexpr (since C++11), consteval (since C++20), inline, or static. 4) The body of the main function does not need to contain the return statement: if control reaches the end of main without encountering a return statement, the effect is that of executing return 0;. 5) Execution of the return (or the implicit return upon reaching the end of main) is equivalent to first leaving the function normally (which destroys the objects with automatic storage duration) and then calling std::exit with the same argument as the argument of the return. (std::exit then destroys static objects and terminates the program). 6) (since C++14) The return type of the main function cannot be deduced (auto main() {... is not allowed). 7) (since C++20) The main function cannot be a coroutine.
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/* simple code example by main() function in C++ */ #include <iostream> using namespace std; int main() { int day = 4; switch (day) { case 1: cout << "Monday"; break; case 2: cout << "Tuesday"; break; case 3: cout << "Wednesday"; break; case 4: cout << "Thursday"; break; case 5: cout << "Friday"; break; case 6: cout << "Saturday"; break; case 7: cout << "Sunday"; break; } return 0; }
Class Templates in C++
Templates are powerful features of C++ which allows us to write generic programs. Similar to function templates, we can use class templates to create a single class to work with different data types. Class templates come in handy as they can make our code shorter and more manageable. A class template starts with the keyword template followed by template parameter(s) inside <> which is followed by the class declaration.
Declaration for Class Template in C++
template <class T> class className { private: T var; ... .. ... public: T functionName(T arg); ... .. ... };
T
template argument
var
a member variable T is the template argument which is a placeholder for the data type used, and class is a keyword. Inside the class body, a member variable var and a member function functionName() are both of type T. Creating a class template object: Once we've declared and defined a class template, we can create its objects in other classes or functions (such as the main() function) with the following syntax:
className<dataType> classObject;
Defining a class member outside the class template: Suppose we need to define a function outside of the class template. We can do this with the following code:
template <class T> class ClassName { ... .. ... // Function prototype returnType functionName(); }; // Function definition template <class T> returnType ClassName<T>::functionName() { // code }
Notice that the code template <class T> is repeated while defining the function outside of the class. This is necessary and is part of the syntax. C++ class templates with multiple parameters: In C++, we can use multiple template parameters and even use default arguments for those parameters.
template <class T, class U, class V = int> class ClassName { private: T member1; U member2; V member3; ... .. ... public: ... .. ... };
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/* Templates are the foundation of generic programming, which involves writing code in a way that is independent of any particular type. A template is a blueprint or formula for creating a generic class or a function. */ #include <iostream> using namespace std; template <typename T> class Array { private: T *ptr; int size; public: Array(T arr[], int s); void print(); }; template <typename T> Array<T>::Array(T arr[], int s) { ptr = new T[s]; size = s; for(int i = 0; i < size; i++) ptr[i] = arr[i]; } template <typename T> void Array<T>::print() { for (int i = 0; i < size; i++) cout<<" "<<*(ptr + i); cout<<endl; } int main() { int arr[5] = {1, 2, 3, 4, 5}; Array<int> a(arr, 5); a.print(); return 0; }
Delete Operator in C++
Deallocate storage space. Default deallocation functions (single-object form). A delete operator is used to deallocate memory space that is dynamically created using the new operator, calloc and malloc() function, etc., at the run time of a program in C++ language. In other words, a delete operator is used to release array and non-array (pointer) objects from the heap, which the new operator dynamically allocates to put variables on heap memory. We can use either the delete operator or delete [ ] operator in our program to delete the deallocated space. A delete operator has a void return type, and hence, it does not return a value.
Syntax for Delete Operator in C++
//ordinary (1) void operator delete (void* ptr) noexcept; //nothrow (2) void operator delete (void* ptr, const std::nothrow_t& nothrow_constant) noexcept; //placement (3) void operator delete (void* ptr, void* voidptr2) noexcept;
ptr
A pointer to the memory block to be released, type-casted to a void*. If this is a null-pointer, the function does nothing. If not null, this pointer value should have been returned by a previous call to operator new, and have not yet been released by a previous call to this function. If the implementation has strict pointer safety, this pointer shall also be a safely-derived pointer.
nothrow_constant
The constant nothrow. This parameter is ignored in the default definition. nothrow_t is the type of constant nothrow.
voidptr2
A void pointer. The value is ignored in the default definition.
size
The first argument passed to the allocation function when the memory block was allocated. std::size_t is an unsigned integral type. This function does not return any value. (1) ordinary delete: Deallocates the memory block pointed by ptr (if not null), releasing the storage space previously allocated to it by a call to operator new and rendering that pointer location invalid. (2) nothrow delete: Same as above (1). The default definition calls the first version (1): ::operator delete(ptr). (3) placement delete: Does nothing. The default allocation and deallocation functions are special components of the standard library; They have the following unique properties: Global: All overloads of operator delete are declared in the global namespace, not within the std namespace. Implicit: The deallocating versions (i.e., all but (3)) are implicitly declared in every translation unit of a C++ program, no matter whether header <new> is included or not. Replaceable: The deallocating versions (i.e., all but (3)) are also replaceable: A program may provide its own definition that replaces the one provided by default or can overload it for specific types. The custom definition shall deallocate the storage referenced by ptr. operator delete is a regular function that can be called explicitly just as any other function. But in C++, delete is an operator with a very specific behavior: An expression with the delete operator, first calls the appropriate destructor (for class types), and then calls a deallocation function. The deallocation function for a class object is a member function named operator delete, if it exists. In all other cases it is a global function operator delete (i.e., this function -- or a more specific overload). If the delete expression is preceded by the scope operator (i.e., ::operator delete), only global deallocation functions are considered. delete expressions that use global deallocation functions always use the signature that takes either a pointer (such as (1)), or a pointer and a size (such as (4)). Preferring always the version with size (4), unless an overload provides a better match for the pointer type. The other signatures ((2) and (3)) are never called by a delete-expression (the delete operator always calls the ordinary version of this function, and exactly once for each of its arguments). These other signatures are only called automatically by a new-expression when their object construction fails (e.g., if the constructor of an object throws while being constructed by a new-expression with nothrow, the matching operator delete function accepting a nothrow argument is called). Non-member deallocation functions shall not be declared in a namespace scope other than the global namespace.
Data races
Modifies the storage referenced by ptr. Calls to allocation and deallocation functions that reuse the same unit of storage shall occur in a single total order where each deallocation happens before the next allocation. This shall also apply to the observable behavior of custom replacements for this function.
Exception safety
No-throw guarantee: this function never throws exceptions. Notice that either an invalid value of ptr, or a value for size that does not match the one passed to the allocation function, causes undefined behavior. Similarly, we can delete the block of allocated memory space using the delete [] operator. delete [ ] pointer_variable; // delete [] ptr; It deallocate for an array.
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/* deallocate storage space by delete operator */ #include <iostream> using namespace std; int main () { // declaration of variables int *ptr1, *ptr2, sum; // allocated memory space using new operator ptr1 = new int; ptr2 = new int; cout << " Enter first number: "; cin >> *ptr1; cout << " Enter second number: "; cin >> *ptr2; sum = *ptr1 + *ptr2; cout << " Sum of pointer variables = " << sum; // delete pointer variables delete ptr1; delete ptr2; return 0; }
While Loop Statement in C++
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
Syntax for While Loop Statement in C++
while (condition) { // body of the loop }
• A while loop evaluates the condition • If the condition evaluates to true, the code inside the while loop is executed. • The condition is evaluated again. • This process continues until the condition is false. • When the condition evaluates to false, the loop terminates. Do not forget to increase the variable used in the condition, otherwise the loop will never end!
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/* While Loop Statement in C++ language */ // program to find the sum of positive numbers // if the user enters a negative number, the loop ends // the negative number entered is not added to the sum #include <iostream> using namespace std; int main() { int number; int sum = 0; // take input from the user cout << "Enter a number: "; cin >> number; while (number >= 0) { // add all positive numbers sum += number; // take input again if the number is positive cout << "Enter a number: "; cin >> number; } // display the sum cout << "\nThe sum is " << sum << endl; return 0; }
For Loop Statement in C++
In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
Syntax of For Loop Statement in C++
for (initialization; condition; update) { // body of-loop }
initialization
initializes variables and is executed only once.
condition
if true, the body of for loop is executed, if false, the for loop is terminated.
update
updates the value of initialized variables and again checks the condition. A new range-based for loop was introduced to work with collections such as arrays and vectors.
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/* For Loop Statement in C++ Language */ // C++ program to find the sum of first n natural numbers // positive integers such as 1,2,3,...n are known as natural numbers #include <iostream> using namespace std; int main() { int num, sum; sum = 0; cout << "Enter a positive integer: "; cin >> num; for (int i = 1; i <= num; ++i) { sum += i; } cout << "Sum = " << sum << endl; return 0; }
Constructors in C++ Language
In C++, constructor is a special method which is invoked automatically at the time of object creation. It is used to initialize the data members of new object generally. The constructor in C++ has the same name as class or structure. Constructors are special class functions which performs initialization of every object. The Compiler calls the Constructor whenever an object is created. Constructors initialize values to object members after storage is allocated to the object. Whereas, Destructor on the other hand is used to destroy the class object. • Default Constructor: A constructor which has no argument is known as default constructor. It is invoked at the time of creating object.
Syntax for Default Constructor in C++
class_name(parameter1, parameter2, ...) { // constructor Definition }
• Parameterized Constructor: In C++, a constructor with parameters is known as a parameterized constructor. This is the preferred method to initialize member data. These are the constructors with parameter. Using this Constructor you can provide different values to data members of different objects, by passing the appropriate values as argument.
Syntax for Parameterized Constructor in C++
class class_name { public: class_name(variables) //Parameterized constructor declared. { } };
• Copy Constructors: These are special type of Constructors which takes an object as argument, and is used to copy values of data members of one object into other object.
Syntax for Copy Constructors in C++
classname (const classname &obj) { // body of constructor }
The copy constructor is a constructor which creates an object by initializing it with an object of the same class, which has been created previously. The copy constructor is used to - • Initialize one object from another of the same type. • Copy an object to pass it as an argument to a function. • Copy an object to return it from a function. If a copy constructor is not defined in a class, the compiler itself defines one.If the class has pointer variables and has some dynamic memory allocations, then it is a must to have a copy constructor. The most common form of copy constructor is shown here.
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/* A constructor is a special type of member function that is called automatically when an object is created. In C++, a constructor has the same name as that of the class and it does not have a return type. */ #include <iostream> using namespace std; // declare a class class Wall { private: double length; double height; public: // initialize variables with parameterized constructor Wall(double len, double hgt) { length = len; height = hgt; } // copy constructor with a Wall object as parameter // copies data of the obj parameter Wall(Wall &obj) { length = obj.length; height = obj.height; } double calculateArea() { return length * height; } }; int main() { // create an object of Wall class Wall wall1(10.5, 8.6); // copy contents of wall1 to wall2 Wall wall2 = wall1; // print areas of wall1 and wall2 cout << "Area of Wall 1: " << wall1.calculateArea() << endl; cout << "Area of Wall 2: " << wall2.calculateArea(); return 0; }


Since Floyd's triangle is right 'angled-triangle' formed by the natural numbers. C++ program ask you to enter the range to print the Floyd's Triangle upto the 'given range'. First enter the
Program ask to the user to enter any number in Hexadecimal to convert it into octal, then display the result on the screen: Here first we will convert the entered hexadecimal number