C++ Programming Code Examples
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Count keys in multimap
/* Count keys in multimap */
#include <iostream>
using std::cout;
using std::endl;
#include <map>
int main()
{
std::multimap< int, double, std::less< int > > pairs; // declare the multimap pairs
cout << "There are currently " << pairs.count( 15 )
<< " pairs with key 15 in the multimap\n";
// insert two value_type objects in pairs
pairs.insert( std::multimap< int, double, std::less< int > >::value_type( 15, 2.7 ) );
pairs.insert( std::multimap< int, double, std::less< int > >::value_type( 15, 99.3 ) );
cout << "After inserts, there are " << pairs.count( 15 )
<< " pairs with key 15\n\n";
cout << endl;
return 0;
}
/*
There are currently 0 pairs with key 15 in the multimap
After inserts, there are 2 pairs with key 15
*/
#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.
Insert element. Extends the container by inserting new elements, effectively increasing the container size by the number of elements inserted. Internally, multimap containers keep all their elements sorted by key following the criterion specified by its comparison object. The elements are always inserted in its respective position following this ordering. The relative ordering of elements with equivalent keys is preserved, and newly inserted elements follow those with equivalent keys already in the container. The parameters determine how many elements are inserted and to which values they are initialized:
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.
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 return statement ends the processing of the current function and returns control to the caller of the function. A value-returning function should include a return statement, containing an expression. If an expression is not given on a return statement in a function declared with a non-void return type, the compiler issues an error message. If the data type of the expression is different from the function return type, conversion of the return value takes place as if the value of the expression were assigned to an object with the same function return type.
Multiple-key map. Multimaps are associative containers that store elements formed by a combination of a key value and a mapped value, following a specific order, and where multiple elements can have equivalent keys. In a multimap, the key values are generally used to sort and uniquely identify the elements, while the mapped values store the content associated to this key. The types of key and mapped value may differ, and are grouped together in member type value_type, which is a pair type combining both. Internally, the elements in a multimap are always sorted by its key following a specific strict weak ordering criterion indicated by its internal comparison object (of type Compare).
Count elements with a specific key. Searches the container for elements with a key equivalent to k and returns the number of matches. Two keys are considered equivalent if the container's comparison object returns false reflexively (i.e., no matter the order in which the keys are passed as arguments). The C++ multimap::count function returns the number of occurrences of a specified key in the multimap container. The function accepts one mandatory parameter key which specifies the key whose count in multimap container is to be returned.
Function object class for less-than inequality comparison. Binary function object class whose call returns whether the its first argument compares less than the second (as returned by operator <). Generically, function objects are instances of a class with member function operator() defined. This member function allows the object to be used with the same syntax as a function call. This function does not return any value.
The operator "=" is an "assignment operator" in C++ and it assigns a value to the objects on the left. C++ Language provides capability to combine assignment operator with almost all
Prints a total number of combination possible for given n and r value. The "time complexity" of this algorithm is O(n). This algorithm takes the input of n and r value. Function to find the
