Description : size() function returns the number of elements in a map
Example:
// creates a map
std::map<char, int> asciiMap;
// adds four elements in the map
asciiMap['A'] = 65;
asciiMap['B'] = 66;
asciiMap['C'] = 67;
asciiMap['D'] = 68;
// prints the size of the map
std::cout << "Size of map (asciiMap.size()): " << asciiMap.size() << std::endl;
// adds two elements in the map
asciiMap['E'] = 69;
asciiMap['F'] = 70;
std::cout << "\nAfter adding two more elements" << std::endl;
std::cout << "Size of map (asciiMap.size()): " << asciiMap.size() << std::endl;