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C++ Programming Code Examples

C++ > Computer Graphics Code Examples

Program to Find Maximum Number of Edge Disjoint Paths

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/* Program to Find Maximum Number of Edge Disjoint Paths This C++ program displays the maximum number of edge disjoint paths present between two vertices. Maximum number of edge disjoint paths refers to the maximum flow or shortest subset path between two vertices. Here is the source code of the C++ program to display the number of paths present between two given vertices on being given a directed graph as input. */ #include <iostream> #include <limits.h> #include <string.h> #include <queue> #include<conio.h> using namespace std; #define V 8 bool bfs(int rGraph[V][V], int s, int t, int parent[]) { bool visited[V]; memset(visited, 0, sizeof(visited)); queue <int> q; q.push(s); visited[s] = true; parent[s] = -1; while (!q.empty()) { int u = q.front(); q.pop(); for (int v = 0; v < V; v++) { if (visited[v] == false && rGraph[u][v] > 0) { q.push(v); parent[v] = u; visited[v] = true; } } } return (visited[t] == true); } int findDisjointPaths(int graph[V][V], int s, int t) { int u, v; int rGraph[V][V]; for (u = 0; u < V; u++) for (v = 0; v < V; v++) { rGraph[u][v] = graph[u][v]; } } int parent[V]; int max_flow = 0; while (bfs(rGraph, s, t, parent)) { int path_flow = INT_MAX; for (v = t; v != s; v = parent[v]) { u = parent[v]; path_flow = min(path_flow, rGraph[u][v]); } for (v = t; v != s; v = parent[v]) { u = parent[v]; rGraph[u][v] -= path_flow; rGraph[v][u] += path_flow; } max_flow += path_flow; } return max_flow; } int main() { int graph[V][V] = { {0, 1, 1, 1, 0, 0, 0, 0}, {0, 0, 1, 0, 0, 0, 0, 0}, {0, 0, 0, 1, 0, 0, 1, 0}, {0, 0, 0, 0, 0, 0, 1, 0}, {0, 0, 1, 0, 0, 0, 0, 1}, {0, 1, 0, 0, 0, 0, 0, 1}, {0, 0, 0, 0, 0, 1, 0, 1}, {0, 0, 0, 0, 0, 0, 0, 0} }; int s = 0; int t = 7; cout << "There can be maximum " << findDisjointPaths(graph, s, t)<< " edge-disjoint paths from " << s <<" to "<<t; getch(); }
Queue in C++ Language
FIFO queue. queues are a type of container adaptor, specifically designed to operate in a FIFO context (first-in first-out), where elements are inserted into one end of the container and extracted from the other. queues are implemented as containers adaptors, which are classes that use an encapsulated object of a specific container class as its underlying container, providing a specific set of member functions to access its elements. Elements are pushed into the "back" of the specific container and popped from its "front". The underlying container may be one of the standard container class template or some other specifically designed container class. This underlying container shall support at least the following operations: • empty • size • front • back • push_back • pop_front The standard container classes deque and list fulfill these requirements. By default, if no container class is specified for a particular queue class instantiation, the standard container deque is used.
Syntax for Queue in C++
template <class T, class Container = deque<T> > class queue;
T
Type of the elements. Aliased as member type queue::value_type.
Container
Type of the internal underlying container object where the elements are stored. Its value_type shall be T. Aliased as member type queue::container_type.
Member Types
Given below is a list of the queue member types with a short description of the same. value_type: Element type is specified. container_type: Underlying container type is specified. size_type: It specifies the size range of the elements. reference: It is a reference type of a container. const_reference: It is a reference type of a constant container.
Member Functions
With the help of functions, an object or variable can be played with in the field of programming. Queues provide a large number of functions that can be used or embedded in the programs. A list of the same is given below: • (constructor): The function is used for the construction of a queue container. • empty: The function is used to test for the emptiness of a queue. If the queue is empty the function returns true else false. • size: The function returns the size of the queue container, which is a measure of the number of elements stored in the queue. • front: The function is used to access the front element of the queue. The element plays a very important role as all the deletion operations are performed at the front element. • back: The function is used to access the rear element of the queue. The element plays a very important role as all the insertion operations are performed at the rear element. • push: The function is used for the insertion of a new element at the rear end of the queue. • pop: The function is used for the deletion of element; the element in the queue is deleted from the front end. • emplace: The function is used for insertion of new elements in the queue above the current rear element. • swap: The function is used for interchanging the contents of two containers in reference. • relational operators: The non member function specifies the relational operators that are needed for the queues. • uses allocator<queue>: As the name suggests the non member function uses the allocator for the queues.
Non-member overloaded functions
• operator== Tests whether two queues are equal or not. • operator!= Tests whether two queues are equal or not. • operator< Tests whether first queue is less than other or not. • operator<= Tests whether first queue is less than or equal to other or not. • operator> Tests whether first queue is greater than other or not. • operator>= Tests whether first queue is greater than or equal to other or not. • swap Exchanges the contents of two queues.
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/* Queue is a data structure designed to operate in FIFO (First in First out) context. In queue elements are inserted from rear end and get removed from front end. Queue class is container adapter. Container is an objects that hold data of same type. Queue can be created from different sequence containers. Container adapters do not support iterators therefore we cannot use them for data manipulation. However they support push() and pop() member functions for data insertion and deletion respectively. */ // CPP code to illustrate // Queue in Standard Template Library (STL) #include <iostream> #include <queue> using namespace std; // Print the queue void showq(queue<int> gq) { queue<int> g = gq; while (!g.empty()) { cout << '\t' << g.front(); g.pop(); } cout << '\n'; } // Driver Code int main() { queue<int> gquiz; gquiz.push(10); gquiz.push(20); gquiz.push(30); cout << "The queue gquiz is : "; showq(gquiz); cout << "\ngquiz.size() : " << gquiz.size(); cout << "\ngquiz.front() : " << gquiz.front(); cout << "\ngquiz.back() : " << gquiz.back(); cout << "\ngquiz.pop() : "; gquiz.pop(); showq(gquiz); return 0; }
#define Directive in C++
In the C++ Programming Language, the #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. Macro definitions are not variables and cannot be changed by your program code like variables. You generally use this syntax when creating constants that represent numbers, strings or expressions. The syntax for creating a constant using #define in the C++ is: #define token value
Syntax for #define Directive in C++
#define macro-name replacement-text
• Using #define to create Macros Macros also follow the same structure as Symbolic Constants; however, Macros allow arguments to be included in the identifier:
#define SQUARE_AREA(l) ((l) * (l))
Unlike in functions, the argument here is enclosed in parenthesis in the identifier and does not have a type associated with it. Before compilation, the compiler will replace every instance of SQUARE_AREA(l) by ((l) * (l)), where l can be any expression. • Conditional Compilation There are several directives, which can be used to compile selective portions of your program's source code. This process is called conditional compilation. The conditional preprocessor construct is much like the 'if' selection structure. Consider the following preprocessor code:
#ifndef NULL #define NULL 0 #endif
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/* #define directive in C++ language */ #include <bits/stdc++.h> using namespace std; void func1(); void func2(); #pragma startup func1 #pragma exit func2 void func1() { cout << "Inside func1()\n"; } void func2() { cout << "Inside func2()\n"; } int main() { void func1(); void func2(); cout << "Inside main()\n"; 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; }
Logical Operators in C++
Logical Operators are used to compare and connect two or more expressions or variables, such that the value of the expression is completely dependent on the original expression or value or variable. We use logical operators to check whether an expression is true or false. If the expression is true, it returns 1 whereas if the expression is false, it returns 0. Assume variable A holds 1 and variable B holds 0:
&&
Called Logical AND operator. If both the operands are non-zero, then condition becomes true. (A && B) is false. The logical AND operator && returns true - if and only if all the operands are true. false - if one or more operands are false.
||
Called Logical OR Operator. If any of the two operands is non-zero, then condition becomes true. (A || B) is true. The logical OR operator || returns true - if one or more of the operands are true. false - if and only if all the operands are false.
!
Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true, then Logical NOT operator will make false. !(A && B) is true. The logical NOT operator ! is a unary operator i.e. it takes only one operand. It returns true when the operand is false, and false when the operand is true.
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/* The operator ! is the C++ operator for the Boolean operation NOT. It has only one operand, to its right, and inverts it, producing false if its operand is true, and true if its operand is false. Basically, it returns the opposite Boolean value of evaluating its operand. The logical operators && and || are used when evaluating two expressions to obtain a single relational result. The operator && corresponds to the Boolean logical operation AND, which yields true if both its operands are true, and false otherwise. */ #include <iostream> using namespace std; main() { int a = 5; int b = 20; int c ; if(a && b) { cout << "Line 1 - Condition is true"<< endl ; } if(a || b) { cout << "Line 2 - Condition is true"<< endl ; } /* Let's change the values of a and b */ a = 0; b = 10; if(a && b) { cout << "Line 3 - Condition is true"<< endl ; } else { cout << "Line 4 - Condition is not true"<< endl ; } if(!(a && b)) { cout << "Line 5 - Condition is true"<< endl ; } return 0; }
IOS Library eof() Function in C++
Check whether eofbit is set. Returns true if the eofbit error state flag is set for the stream. This flag is set by all standard input operations when the End-of-File is reached in the sequence associated with the stream. Note that the value returned by this function depends on the last operation performed on the stream (and not on the next). Operations that attempt to read at the End-of-File fail, and thus both the eofbit and the failbit end up set. This function can be used to check whether the failure is due to reaching the End-of-File or to some other reason.
Syntax for IOS eof() Function in C++
bool eof() const;
This function does not accept any parameter. Function returns true if the stream's eofbit error state flag is set (which signals that the End-of-File has been reached by the last input operation). false otherwise.
Data races
Accesses the stream object. Concurrent access to the same stream object may cause data races.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the stream.
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/* The eof() method of ios class in C++ is used to check if the stream is has raised any EOF (End Of File) error. It means that this function will check if this stream has its eofbit set. */ // C++ code example to demonstrate the working of eof() function #include <iostream> #include <fstream> int main () { std::ifstream is("example.txt"); char c; while (is.get(c)) std::cout << c; if (is.eof()) std::cout << "[EoF reached]\n"; else std::cout << "[error reading]\n"; is.close(); return 0; }
getch() Function in C++
The getch() is a predefined non-standard function that is defined in conio.h header file. It is mostly used by the Dev C/C++, MS- DOS's compilers like Turbo C to hold the screen until the user passes a single value to exit from the console screen. It can also be used to read a single byte character or string from the keyboard and then print. It does not hold any parameters. It has no buffer area to store the input character in a program.
Syntax for getch() Function in C++
#include <conio.h> int getch(void);
The getch() function does not accept any parameter from the user. It returns the ASCII value of the key pressed by the user as an input. We use a getch() function in a C/ C++ program to hold the output screen for some time until the user passes a key from the keyboard to exit the console screen. Using getch() function, we can hide the input character provided by the users in the ATM PIN, password, etc. • getch() method pauses the Output Console until a key is pressed. • It does not use any buffer to store the input character. • The entered character is immediately returned without waiting for the enter key. • The entered character does not show up on the console. • The getch() method can be used to accept hidden inputs like password, ATM pin numbers, etc.
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/* wait for any character input from keyboard by getch() function code example. The getch() function is very useful if you want to read a character input from the keyboard. */ // C code to illustrate working of // getch() to accept hidden inputs #include<iostream.h> #include<conio.h> void main() { int a=10, b=20; int sum=0; clrscr(); sum=a+b; cout<<"Sum: "<<sum; getch(); // use getch() befor end of main() }
Queue Library front() Function in C++
Access next element. Returns a reference to the next element in the queue. The next element is the "oldest" element in the queue and the same element that is popped out from the queue when queue::pop is called. This member function effectively calls member front of the underlying container object. In C++ STL, Queue is a type of container that follows FIFO (First-in-First-Out) elements arrangement i.e. the elements which insert first will be removed first. In queue, elements are inserted at one end known as "back" and are deleted from another end known as "front". The function front() returns the reference to the first element in the queue i.e. the oldest element in the queue, so it is used to get the first element from the front of the list of a queue.
Syntax for Queue front() Function in C++
#include <queue> reference& front(); const_reference& front() const;
This function does not accept any parameter. Function returns a reference to the next element in the queue. Member types reference and const_reference are aliases of the underlying container's types with the same name.
Complexity
Constant (calling front on the underlying container).
Data races
The container is accessed (neither the const nor the non-const versions modify the container). The reference returned can be used to access or modify the next element.
Exception safety
Provides the same level of guarantees as the operation performed on the container (no-throw guarantee for standard non-empty containers).
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/* C++ Queue front() function returns the value of the front element of the queue. The first element is the oldest element or the element which was initially added to the queue. The function is used to return that element. */ /* reference the first or the oldest element of the queue container by Queue front() function code example. */ #include <iostream> #include <queue> using namespace std; int main (){ queue<int> MyQueue; MyQueue.push(10); MyQueue.push(20); MyQueue.push(30); MyQueue.push(40); MyQueue.push(50); cout<<"The first element of MyQueue is: "; cout<<MyQueue.front(); cout<<"\n\nDelete the oldest element of the MyQueue.\n"; MyQueue.pop(); cout<<"Now, The first element of MyQueue is: "; cout<<MyQueue.front(); return 0; }
Queue Library push() Function in C++
Inserts a new element at the end of the queue, after its current last element. The content of this new element is initialized to val. This member function effectively calls the member function push_back of the underlying container object. In C++ STL, Queue is a type of container that follows FIFO (First-in-First-Out) elements arrangement i.e. the elements which insert first will be removed first. In queue, elements are inserted at one end known as "back" and are deleted from another end known as "front". In the Data Structure, "push" is an operation to insert an element in any container, "pop" is an operation to remove an element from the container. push() inserts an element to queue at the back. After executing this function, element inserted in the queue and its size increased by 1.
Syntax for Queue push() Function in C++
#include <queue> void push (const value_type& val); void push (value_type&& val);
val
Value to which the inserted element is initialized. Member type value_type is the type of the elements in the container (defined as an alias of the first class template parameter, T). This function does not return any value.
Complexity
One call to push_back on the underlying container.
Data races
The container and up to all its contained elements are modified.
Exception safety
Provides the same level of guarantees as the operation performed on the underlying container object.
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/* The C++ function std::queue::push() inserts new element at the end of queue and assigns val to newly inserted element. This member function increases size of queue by one. */ // CPP program code example to illustrate application of push() and pop() function #include <iostream> #include <queue> using namespace std; int main() { // Empty Queue int c = 0; queue<int> myqueue; myqueue.push(5); myqueue.push(13); myqueue.push(0); myqueue.push(9); myqueue.push(4); // queue becomes 5, 13, 0, 9, 4 // Counting number of elements in queue while (!myqueue.empty()) { myqueue.pop(); c++; } cout << c; }
#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; }
memset() Function in C++
Fill block of memory. Sets the first num bytes of the block of memory pointed by ptr to the specified value (interpreted as an unsigned char). This function converts the value of a character to unsigned character and copies it into each of first num character of the object pointed by the given str[]. If the num is larger than string size, it will be undefined.
Syntax for memset() Function in C++
#include <cstring> void * memset ( void * ptr, int value, size_t num );
ptr
Pointer to the block of memory to fill.
value
Value to be set. The value is passed as an int, but the function fills the block of memory using the unsigned char conversion of this value.
num
Number of bytes to be set to the value. size_t is an unsigned integral type. ptr is returned. • Initially, it converts the value of 'value' to the unsigned character. Here 'value' refers to the character to be filled with another value passed in the memset ( ) function. • After then it copies the character 'value' into each of the first 'num' characters of the object pointed by the ptr [ ]. • Here the 'num' is referred to as the size of the block, which is mentioned in the memset ( ), and it must be equal or smaller with the size of the object pointed by ptr [ ]. • If the value of num is greater than the size of the object pointed by the ptr [ ], it will generate error hence undefined. • If sometimes, a case arises where the object is not copyable, then also it will generate an error, and the behavior of the function is the same as in the previous case, i.e., undefined. • In the C++ programming language, the memset ( ) function is present in the < cstring > header file; without mentioning this header file, you would not be able to access the use of the memset ( ) function. • Here, the object which is not copy-able is as follows: array, C-compatible struct, scalar, and so on; hence the behavior of memset ( ) function is undefined in this case. • The only difference between the memset ( ) function and the memcpy ( ) function is that in memset ( ) function not only copies the value but replace it with the other substitute, e.g., if we want to replace each character of a particular string-like, ' cool ', with the alphabet ' f ', then; as a result, and it would be looking at final is; ' ffff '. But in memcpy ( ) function, it only copies the value from one place to another or copies a block of content from a particular place and puts it on another block of content.
Advantages of memset() Function
• Increase readability: The memset ( ) function in C++ is mainly used to convert every character of the whole string into a particular int value which is passed as an input into the memset ( ) function. It is a one-line code; hence very short and ultimately increases the readability. • Reduce line of code: Instead of using unnecessary use of loops to assign and convert the value of each character present in the string with the int value, which is only passed as an input in this memset ( ) function, and the same task has been performed easily as compared with the lengthy method. • It is more Faster: Using the memset ( ) function is faster to convert each character of the given string into the value passed through an input, maybe of int type or any other, depending on the programmer. Its working is very fast rather than applying loops and while statements for performing the same task. • Useful in getting rid of Misalignment Problem: The memset ( ) function in C++ helps the programmer to get rid of misalignment problem. Sometimes, the case occurs where you find that you are dealing with the problem of misalignment of data in the processor, which leads to the error in the program. In this case, the memset ( ) and memcpy ( ) functions in C++ are the ultimate solutions of it.
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/* The memset() function in C++ copies a single character for a specified number of time to an object. */ /* Fill block of memory by memset() function code example */ #include <bits/stdc++.h> using namespace std; int main() { int a[5]; // all elements of A are zero memset(a, 0, sizeof(a)); for (int i = 0; i < 5; i++) cout << a[i] << " "; cout << endl; // all elements of A are -1 memset(a, -1, sizeof(a)); for (int i = 0; i < 5; i++) cout << a[i] << " "; cout << endl; // Would not work memset(a, 5, sizeof(a)); // WRONG for (int i = 0; i < 5; i++) cout << a[i] << " "; }
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; }
Queue Library pop() Function in C++
Remove next element. Removes the next element in the queue, effectively reducing its size by one. The element removed is the "oldest" element in the queue whose value can be retrieved by calling member queue::front. This calls the removed element's destructor. This member function effectively calls the member function pop_front of the underlying container object. C++ Queue pop() function is used for removing the topmost element of the queue. The function is implied only for deletion of elements.
Syntax for Queue pop() Function in C++
#include <queue> void pop();
The function only performs the deletion operation and does not accept any parameters. There is no return value for this function; it is only implied for deletion of elements.
Complexity
Constant (calling pop_front on the underlying container).
Data races
The container and up to all its contained elements are modified.
Exception safety
Provides the same level of guarantees as the operation performed on the underlying container object.
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/* queue pop() function is used to remove an element from the front of the queue(oldest element in the queue). This is an inbuilt function from C++ Standard Template Library(STL). This function belongs to the <queue> header file. The element is removed from the queue container and the size of the queue is decreased by 1. */ // CPP program code example to illustrate implementation of pop() function #include <iostream> #include <queue> using namespace std; int main() { // Empty Queue queue<int> myqueue; myqueue.push(0); myqueue.push(1); myqueue.push(2); // queue becomes 0, 1, 2 myqueue.pop(); myqueue.pop(); // queue becomes 2 // Printing content of queue while (!myqueue.empty()) { cout << ' ' << myqueue.front(); myqueue.pop(); } }
Queue Library empty() Function in C++
Test whether container is empty. Returns whether the queue is empty: i.e. whether its size is zero. This member function effectively calls member empty of the underlying container object. Sometimes before actually starting the work with the individual elements of the containers, it is more feasible to look up if the container is empty, so this function finds its usage in such cases. queue::empty() is an inbuilt function in C++ STL which is declared in header file. queue::empty() is used to check whether the associated queue container is empty or not. This function returns either true or false, if the queue is empty (size is 0) then the function returns true, else if the queue is having some value then it will return false.
Syntax for Queue empty() Function in C++
#include <queue> bool empty() const;
There are no parameters. The function is only used to test for the emptiness of the container and hence takes no parameter. If the container under reference is empty, then the method returns 'true' else returns 'false'.
Complexity
Constant (calling empty on the underlying container).
Data races
The container is accessed.
Exception safety
Provides the same level of guarantees as the operation performed on the container (no-throw guarantee for standard container types).
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/* Test whether container is empty by queue::empty function code example */ /* The queue.empty() function in C++ returns a true (1) value if the queue is empty. Otherwise, it returns false (0). In short, this function is used to check if the queue is empty or not. */ #include <iostream> #include <queue> using namespace std; int main (){ queue<int> MyQueue; cout<<boolalpha; cout<<"Is the Queue empty?: "<<MyQueue.empty()<<"\n"; cout<<"Add elements in the Queue.\n"; MyQueue.push(10); MyQueue.push(20); MyQueue.push(30); cout<<"Now, Is the Queue empty?: "<<MyQueue.empty()<<"\n"; return 0; }
Namespaces in C++ Language
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code. A namespace is designed to overcome this difficulty and is used as additional information to differentiate similar functions, classes, variables etc. with the same name available in different libraries. Using namespace, you can define the context in which names are defined. In essence, a namespace defines a scope.
Defining a Namespace
A namespace definition begins with the keyword namespace followed by the namespace name as follows:
namespace namespace_name { // code declarations }
To call the namespace-enabled version of either function or variable, prepend (::) the namespace name as follows:
name::code; // code could be variable or function.
Using Directive
You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace.
Discontiguous Namespaces
A namespace can be defined in several parts and so a namespace is made up of the sum of its separately defined parts. The separate parts of a namespace can be spread over multiple files. So, if one part of the namespace requires a name defined in another file, that name must still be declared. Writing a following namespace definition either defines a new namespace or adds new elements to an existing one:
namespace namespace_name { // code declarations }
Nested Namespaces
Namespaces can be nested where you can define one namespace inside another name space as follows:
namespace namespace_name1 { // code declarations namespace namespace_name2 { // code declarations } }
• Namespace is a feature added in C++ and not present in C. • A namespace is a declarative region that provides a scope to the identifiers (names of the types, function, variables etc) inside it. • Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope. • Namespace declarations appear only at global scope. • Namespace declarations can be nested within another namespace. • Namespace declarations don't have access specifiers. (Public or private) • No need to give semicolon after the closing brace of definition of namespace. • We can split the definition of namespace over several units.
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/* namespaces in C++ language */ // A C++ code to demonstrate that we can define // methods outside namespace. #include <iostream> using namespace std; // Creating a namespace namespace ns { void display(); class happy { public: void display(); }; } // Defining methods of namespace void ns::happy::display() { cout << "ns::happy::display()\n"; } void ns::display() { cout << "ns::display()\n"; } // Driver code int main() { ns::happy obj; ns::display(); obj.display(); return 0; }
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; }
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; }
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; }
Algorithm Library min() Function in C++
Return the smallest. Returns the smallest of a and b. If both are equivalent, a is returned. min() function is a library function of algorithm header, it is used to find the smallest value from given two values, it accepts two values and returns the smallest value and if both the values are the same it returns the first value. The versions for initializer lists (3) return the smallest of all the elements in the list. Returning the first of them if these are more than one. The function uses operator< (or comp, if provided) to compare the values.
Syntax for Algorithm min() Function in C++
#include <algorithm> //default (1) template <class T> const T& min (const T& a, const T& b); //custom (2) template <class T, class Compare> const T& min (const T& a, const T& b, Compare comp); //initializer list (3) template <class T> T min (initializer_list<T> il); template <class T, class Compare> T min (initializer_list<T> il, Compare comp);
a, b
Values to compare
comp
Binary function that accepts two values of type T as arguments, and returns a value convertible to bool. The value returned indicates whether the element passed as first argument is considered less than the second. The function shall not modify any of its arguments. This can either be a function pointer or a function object.
il
An initializer_list object. These objects are automatically constructed from initializer list declarators. T shall support being compared with operator<. For (3), T shall be copy constructible. Function returns the lesser of the values passed as arguments.
Complexity
Linear in one less than the number of elements compared (constant for (1) and (2)).
Exceptions
Throws if any comparison throws. Note that invalid arguments cause undefined behavior.
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/* std::min is defined in the header file <algorithm> and is used to find out the smallest of the number passed to it. It returns the first of them, if there are more than one. */ /* accept two values and return the smaller one by min() function code example. */ #include <iostream> #include <algorithm> using namespace std; // Defining the binary function bool comp(int a, int b) { return (a < b); } int main() { int a = 5; int b = 7; cout << std::min(a, b, comp) << "\n"; // Returns the first one if both the numbers // are same cout << std::min(7, 7, comp); return 0; }
What is an Multi-Dimensional Array
An array is a collection of data items, all of the same type, accessed using a common name. A one-dimensional array is like a list; A two dimensional array is like a table; The C++ language places no limits on the number of dimensions in an array, though specific implementations may. Some texts refer to one-dimensional arrays as vectors, two-dimensional arrays as matrices, and use the general term arrays when the number of dimensions is unspecified or unimportant.
Declaring Two-Dimensional Arrays
An array of arrays is known as 2D array. The two dimensional (2D) array in C++ programming is also known as matrix. A matrix can be represented as a table of rows and columns. In C/C++, we can define multi dimensional arrays in simple words as array of arrays. Data in multi dimensional arrays are stored in tabular form (in row major order). General form of declaring N-dimensional arrays is:
datatype arrayname[size1][size2]....[sizeN]; example: int 2d-array[8][16]; char letters[4][9]; float numbers[10][25];
Initializing Two-Dimensional Arrays
In the 1D array, we don't need to specify the size of the array if the declaration and initialization are being done simultaneously. However, this will not work with 2D arrays. We will have to define at least the second dimension of the array. The two-dimensional array can be declared and defined in the following way. Multidimensional arrays may be initialized by specifying bracketed values for each row. Following is an array with 3 rows and each row has 4 columns.
int numbers[3][4] = {{0, 1, 2, 3}, {4, 5, 6, 7}, {8, 9, 10, 11}};
Accessing Two-Dimensional Array Elements
Just like one-dimensional arrays, two-dimensional arrays also require indices to access the required elements. A row and a column index are needed to access a particular element; for nested loops, two indices (one to traverse the rows and the other to traverse the columns in each row) are required to print a two-dimensional array.
// an array with 3 rows and 2 columns. int x[3][2] = {{0,1}, {2,3}, {4,5}}; // output each array element's value for (int i = 0; i < 3; i++) { for (int j = 0; j < 2; j++) { cout << "Element at x[" << i << "][" << j << "]: "; cout << x[i][j]<<endl; } }
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/* multi-dimensional arrays in C++ language */ /* taking input for two dimensional array */ #include <iostream> using namespace std; int main() { int numbers[2][3]; cout << "Enter 6 numbers: " << endl; // Storing user input in the array for (int i = 0; i < 2; ++i) { for (int j = 0; j < 3; ++j) { cin >> numbers[i][j]; } } cout << "The numbers are: " << endl; // Printing array elements for (int i = 0; i < 2; ++i) { for (int j = 0; j < 3; ++j) { cout << "numbers[" << i << "][" << j << "]: " << numbers[i][j] << endl; } } return 0; }
Assignment Operators in C++
As the name already suggests, these operators help in assigning values to variables. These operators help us in allocating a particular value to the operands. The main simple assignment operator is '='. We have to be sure that both the left and right sides of the operator must have the same data type. We have different levels of operators. Assignment operators are used to assign the value, variable and function to another variable. Assignment operators in C are some of the C Programming Operator, which are useful to assign the values to the declared variables. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=. The following table lists the assignment operators supported by the C language:
=
Simple assignment operator. Assigns values from right side operands to left side operand
+=
Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.
-=
Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.
*=
Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.
/=
Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.
%=
Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.
<<=
Left shift AND assignment operator.
>>=
Right shift AND assignment operator.
&=
Bitwise AND assignment operator.
^=
Bitwise exclusive OR and assignment operator.
|=
Bitwise inclusive OR and assignment operator.
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/* Assignment operators are used to assigning value to a variable. The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. The value on the right side must be of the same data-type of the variable on the left side otherwise the compiler will raise an error. */ // C++ program to demonstrate working of Assignment operators #include <iostream> using namespace std; int main() { // Assigning value 10 to a // using "=" operator int a = 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by adding 10 to a // using "+=" operator a += 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by subtracting 10 from a // using "-=" operator a -= 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by multiplying 10 to a // using "*=" operator a *= 10; cout << "Value of a is "<<a<<"\n"; // Assigning value by dividing 10 from a // using "/=" operator a /= 10; cout << "Value of a is "<<a<<"\n"; return 0; }
sizeof() Operator in C++
The sizeof() is an operator that evaluates the size of data type, constants, variable. It is a compile-time operator as it returns the size of any variable or a constant at the compilation time. The size, which is calculated by the sizeof() operator, is the amount of RAM occupied in the computer. The sizeof is a keyword, but it is a compile-time operator that determines the size, in bytes, of a variable or data type. The sizeof operator can be used to get the size of classes, structures, unions and any other user defined data type.
Syntax for sizeof() Operator in C++
sizeof(data_type);
data_type
data type whose size is to be calculated The data_type can be the data type of the data, variables, constants, unions, structures, or any other user-defined data type. If the parameter of a sizeof() operator contains the data type of a variable, then the sizeof() operator will return the size of the data type. sizeof() may give different output according to machine, we have run our program on 32 bit gcc compiler.
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/* The sizeof() is an operator in C and C++. It is an unary operator which assists a programmer in finding the size of the operand which is being used. */ #include <iostream> using namespace std; int main() { int arr[]={10,20,30,40,50}; std::cout << "Size of the array 'arr' is : "<<sizeof(arr) << std::endl; cout << "Size of char : " << sizeof(char) << endl; cout << "Size of int : " << sizeof(int) << endl; cout << "Size of short int : " << sizeof(short int) << endl; cout << "Size of long int : " << sizeof(long int) << endl; cout << "Size of float : " << sizeof(float) << endl; cout << "Size of double : " << sizeof(double) << endl; cout << "Size of wchar_t : " << sizeof(wchar_t) << endl; return 0; }


Alphabets a, e, i, o, u are known as vowels. All other alphabets except these 5 alphabets are known are 'consonants'. C++ sample assumes that the user will enter an Alphabet. Similarly