C++ Programming Code Examples
C++ > Beginners Lab Assignments Code Examples
C++ Program to Implement Multiset in STL
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/* C++ Program to Implement Multiset in STL
This C++ Program demonstrates implementation of Multiset in STL. */
#include <iostream>
#include <set>
#include <string>
#include <cstdlib>
using namespace std;
int main()
{
multiset<int> ms;
multiset<int>::iterator it, it1;
int choice, item;
while (1)
{
cout<<"\n---------------------"<<endl;
cout<<"Multiset Implementation in Stl"<<endl;
cout<<"\n---------------------"<<endl;
cout<<"1.Insert Element into the Multiset"<<endl;
cout<<"2.Delete Element from the Multiset"<<endl;
cout<<"3.Find Element in a Multiset"<<endl;
cout<<"4.Count Elements with a specific key"<<endl;
cout<<"5.Size of the Multiset"<<endl;
cout<<"6.Display Multiset"<<endl;
cout<<"7.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>choice;
switch(choice)
{
case 1:
cout<<"Enter value to be inserted: ";
cin>>item;
if (ms.empty())
it1 = ms.insert(item);
else
it1 = ms.insert(it1, item);
break;
case 2:
cout<<"Enter value to be deleted: ";
cin>>item;
ms.erase(item);
break;
case 3:
cout<<"Enter element to find ";
cin>>item;
it = ms.find(item);
if (it != ms.end())
cout<<"Element found"<<endl;
else
cout<<"Element not found"<<endl;
break;
case 4:
cout<<"Enter element to be counted: ";
cin>>item;
cout<<item<<" appears "<<ms.count(item)<<" times."<<endl;
break;
case 5:
cout<<"Size of the Multiset: "<<ms.size()<<endl;
break;
case 6:
cout<<"Elements of the Multiset: ";
for (it = ms.begin(); it != ms.end(); it++)
cout<<*it<<" ";
cout<<endl;
break;
case 7:
exit(1);
break;
default:
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}
Return container size. Returns the number of elements in the multiset container. C++ Multiset size() function is used to find the number of elements present in the multiset container. size() function returns the number of elements in the container, i.e. std::distance(begin(), end()). No parameter is required.
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.
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.
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.
Return iterator to beginning. Returns an iterator referring to the first element in the multiset container. The multiset::begin() is a built-in function in C++ STL which returns an iterator pointing to the first element in the multiset container. Since multiset always contains elements in an ordered way, begin() always points to the first element according to the sorting criterion. Because multiset containers keep their elements ordered at all times, begin points to the element that goes first following the container's sorting criterion. If the container is empty, the returned iterator value shall not be dereferenced. This function does not accept any parameter.
Insert element. Extends the container by inserting new elements, effectively increasing the container size by the number of elements inserted. Internally, multiset containers keep all their elements sorted following the criterion specified by its comparison object. The elements are always inserted in its respective position following this ordering. The relative ordering of equivalent elements is preserved, and newly inserted elements follow their equivalents already in the container. The parameters determine how many elements are inserted and to which values they are initialized: The function optimizes its insertion time if position points to the element that will follow the inserted element (or to the end, if it would be the last). Notice that this is just a hint and does not force the new element to be inserted at that position within the multiset container (the elements in a multiset always follow a specific order).
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.
Test whether container is empty. Returns whether the multiset container is empty (i.e. whether its size is 0). The multiset::empty() function is a built-in function in C++ STL which checks if the multiset is empty or not. It returns true if the multiset is empty, else it returns false. This function does not modify the container in any way. To clear the content of a multiset container, see multiset::clear.
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.
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Iterators are just like pointers used to access the container elements. Iterators are one of the four pillars of the Standard Template Library or STL in C++. An iterator is used to point to the memory address of the STL container classes. For better understanding, you can relate them with a pointer, to some extent. Iterators act as a bridge that connects algorithms to STL containers and allows the modifications of the data present inside the container. They allow you to iterate over the container, access and assign the values, and run different operators over them, to get the desired result. • Iterators are used to traverse from one element to another element, a process is known as iterating through the container. • The main advantage of an iterator is to provide a common interface for all the containers type. • Iterators make the algorithm independent of the type of the container used.
Erase elements. Removes elements from the multiset container. The multiset::erase() is the STL function in C++ removes the specified element from multiset. This effectively reduces the container size by the number of elements removed, which are destroyed. The parameters determine the elements removed: Member types iterator and const_iterator are bidirectional iterator types that point to elements. The erase() function returns an iterator that point to the next element of the deleted element or returns the number of deleted elements.
Get iterator to element. Searches the container for an element equivalent to val and returns an iterator to it if found, otherwise it returns an iterator to multiset::end. The C++ multiset::find function is used to search the container for an element equivalent to the specified value and returns the iterator to it if found, else returns the iterator to multiset::end. Notice that this function returns an iterator to a single element (of the possibly multiple equivalent elements). To obtain the entire range of equivalent elements, see multiset::equal_range. Two elements of a multiset are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the elements are passed as arguments).
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Return iterator to end. Returns an iterator referring to the past-the-end element in the multiset container. The multiset::end() is a built-in function in C++ STL which returns an iterator pointing to the position past the last element in the container. The past-the-end element is the theoretical element that would follow the last element in the multiset container. It does not point to any element, and thus shall not be dereferenced. Because the ranges used by functions of the standard library do not include the element pointed by their closing iterator, this function is often used in combination with multiset::begin to specify a range including all the elements in the container.
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.
Count elements with a specific key. Searches the container for elements equivalent to val and returns the number of matches. Two elements of a multiset are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the elements are passed as arguments). C++ Multiset count() function is used to return the number of elements found in the container. Since, the multiset container does not contain any duplicate element, this function actually returns 1 if the element with value val is present in the multiset container otherwise, it returns 0. Function returns the number of elements in the container that are equivalent to val.
Multiple-key set. Multisets are containers that store elements following a specific order, and where multiple elements can have equivalent values. Multisets are part of the C++ STL (Standard Template Library). Multisets are the associative containers like Set that stores sorted values (the value is itself the key, of type T), but unlike Set which store only unique keys, multiset can have duplicate keys. By default it uses < operator to compare the keys. The value of the elements in a multiset can be inserted or deleted but cannot be altered (The elements are always const). In a multiset, the value of an element also identifies it (the value is itself the key, of type T). The value of the elements in a multiset cannot be modified once in the container (the elements are always const), but they can be inserted or removed from the container.
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