multimap equal_range() in C++ STL

The multimap::equal_range() is a built-in function in C++ STL which returns an iterator of pairs. The pair refers to the bounds of a range that includes all the elements in the container which have a key equivalent to k. If there are no matches with key K, the range returned is of length 0 with both iterators pointing to the first element that has a key considered to go after k according to the container's internal comparison object (key_comp). 

Syntax:  

iterator multimap_name.equal_range(key)

Parameters: This function accepts a single mandatory parameter key which specifies the element whose range in the container is to be returned. 

Return Value: The function returns an iterator of pairs. The pair refers to the bounds of a range that includes all the elements in the container which have a key equivalent to k. If there are no matches with key K, the range returned is of length 0 with both iterators pointing to the first element that has a key considered to go after k according to the container's internal comparison object (key_comp).

Program below illustrate the above method:  

The multimap elements of key 1 is : 
KEY ELEMENT
1 40
1 20