C++ Programming Code Examples
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Program to Implement Queue in STL
/* Program to Implement Queue in STL
This C++ Program demonstrates implementation of Queue in STL. */
#include <iostream>
#include <queue>
#include <string>
#include <cstdlib>
using namespace std;
int main()
{
queue<int> q;
int choice, item;
while (1)
{
cout<<"\n---------------------"<<endl;
cout<<"Queue Implementation in Stl"<<endl;
cout<<"\n---------------------"<<endl;
cout<<"1.Insert Element into the Queue"<<endl;
cout<<"2.Delete Element from the Queue"<<endl;
cout<<"3.Size of the Queue"<<endl;
cout<<"4.Front Element of the Queue"<<endl;
cout<<"5.Last Element of the Queue"<<endl;
cout<<"6.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>choice;
switch(choice)
{
case 1:
cout<<"Enter value to be inserted: ";
cin>>item;
q.push(item);
break;
case 2:
item = q.front();
q.pop();
cout<<"Element "<<item<<" Deleted"<<endl;
break;
case 3:
cout<<"Size of the Queue: ";
cout<<q.size()<<endl;
break;
case 4:
cout<<"Front Element of the Queue: ";
cout<<q.front()<<endl;
break;
case 5:
cout<<"Back Element of the Queue: ";
cout<<q.back()<<endl;
break;
case 6:
exit(1);
break;
default:
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}
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.
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.
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.
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:
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.
Switch statement in C tests the value of a variable and compares it with multiple cases. Once the case match is found, a block of statements associated with that particular case is executed. Each case in a block of a switch has a different name/number which is referred to as an identifier. The value provided by the user is compared with all the cases inside the switch block until the match is found. If a case match is NOT found, then the default statement is executed, and the control goes out of the switch block. • The expression can be integer expression or a character expression. • Value-1, 2, n are case labels which are used to identify each case individually. Remember that case labels should not be same as it may create a problem while executing a program. Suppose we have two cases with the same label as '1'. Then while executing the program, the case that appears first will be executed even though you want the program to execute a second case. This creates problems in the program and
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. 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.
Access last element. Returns a reference to the last element in the queue. This is the "newest" element in the queue (i.e. the last element pushed into the queue). This function is used to reference the last or the newest element of the queue container. This function can be used to fetch the first element from the back of a queue. This member function effectively calls member back of the underlying container object. The function does not take any parameters.
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.
#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.
Break statement in C++ is a loop control statement defined using the break keyword. It is used to stop the current execution and proceed with the next one. When a compiler calls the break statement, it immediately stops the execution of the loop and transfers the control outside the loop and executes the other statements. In the case of a nested loop, break the statement stops the execution of the inner loop and proceeds with the outer loop. The statement itself says it breaks the loop. When the break statement is called in the program, it immediately terminates the loop and transfers the flow control to the statement mentioned outside the loop.
Return size. Returns the number of elements in the queue. This member function effectively calls member size of the underlying container object. The number of elements in the queue is an actual representation of the size, and the size value is given by this function. size() function is used to return the size of the list container or the number of elements in the list container.
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. 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.
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++.
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.
The exit function terminates the program normally. Automatic objects are not destroyed, but static objects are. Then, all functions registered with atexit are called in the opposite order of registration. The code is returned to the operating system. An exit code of 0 or EXIT_SUCCESS means successful completion. If code is EXIT_FAILURE, an indication of program failure is returned to the operating system. Other values of code are implementation-defined. Calls all functions registered with the atexit() function, and destroys C++ objects with static storage duration, all in last-in-first-out (LIFO) order. C++ objects with static storage duration are destroyed in the reverse order of the completion of their constructor. (Automatic objects are not destroyed as a result of calling exit().)
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