How to find a value associated with key in C++?

-2 -> 'A'
-1 -> 'A'
0 -> 'A'
1 -> 'B'
2 -> 'B'
3 -> 'A'
4 -> 'A'
5 -> 'A'

<pre>#include <iostream>
#include <map>


class interval_map {
	friend void IntervalMapTest();
	V m_valBegin;
	typedef std::map<K,V> m_map;
	
public:
	// constructor associates whole range of K with val
	interval_map(V const& val)
	: m_valBegin(val)
	{}

	// Assign value val to interval [keyBegin, keyEnd).
	// Overwrite previous values in this interval.
	// Conforming to the C++ Standard Library conventions, the interval
	// includes keyBegin, but excludes keyEnd.
	// If !( keyBegin < keyEnd ), this designates an empty interval,
	// and assign must do nothing.
void assign( K const& keyBegin, K const& keyEnd, V const& val )
{
    for( auto it = m_map.find( keyBegin ); * it != keyEnd; ++it )
    {
        * it = val;
    }
}

	// look-up of the value associated with key
	V const& operator[]( K const& key ) const {
		auto it=m_map.upper_bound(key);
		if(it==m_map.begin()) {
			return m_valBegin;
		} else {
			return (--it)->second;
		}
	}
};

int main()
{
    m_map map;
    m_map::iterator mpIter;
    
    int keyEnd, keyBegin;
    int count;
    
    // keep track of values with a std::set
    std::set<std::string> values;

    for(count = 0; count < 3; count++)
    {
        cin >> key;
        cin >> value;

        auto found = map.find(key);

        if(found != map.end()) // key already in map
            continue; // don't add it again

        // now try to add it to the set
        // only add to the map if its value is not already in the set
        if(values.insert(value).second)
            map.insert(std::make_pair(key, value));
    }

    
    return 0;
}