What is C# equivalent of <map> in C++?

The equivalent would be class SortedDictionary<TKey, TValue> in the System.Collections.Generic namespace.

If you don't care about the order the class Dictionary<TKey, TValue> in the System.Collections.Generic namespace would probably be sufficient.

std::map<Key, Value> → SortedDictionary<TKey, TValue>

std::unordered_map<Key, Value> → Dictionary<TKey, TValue>

Take a look at the Dictionary class in System::Collections::Generic.

Dictionary<myComplex, int> myMap = new Dictionary<myComplex, int>();