Evaluating expression tree using std::map<std::string, int>

I am not sure how to use the map function to evaluate my tree expression. the function goes like this

Code:

int Tree::evaluate(std::map< std::string, int > ipMap){

and my teacher gave me a hint to look at my function to postorder print for an example but i am not sure how it applies to this. Here it is:

Code:

void Tree::postOrderPrint(){

Code:

void Tree::postOrderPrint(){
    if(NodeType==TYPE_OPERATOR)
    {
        leftPtr->postOrderPrint();
        rightPtr->postOrderPrint();
        std::cout<< Op << "  " ;
    }
    else
    {
        std::cout<< Op << "  " ;
    }


}

what ive tried was wrong. but im just supposed to use map to find if the element in the tree expression is a + - * or / i believe, and if so use that operator to evaluate the left aand right subtrees. Keep in mind that the string is parsed and the tree is already buit

std::map is not a function, it's a container.
That evaluate function is simply asking for you to provide a map as its argument.
So what have you tried, and what went wrong?