C++ PLEASE!

Postfix notation is an unambiguous way of writing an arithmetic expression without parentheses. It is defined so that if (exp1 ) (exp2 ) is a normal (infix) fully parenthesized expression with operation , then its postfix equivalent is pexp1 pexp2 , where pexp1 is the postfix version of exp1 and pexp2 is the postfix version of exp2 . The postfix version of a single number of variables is just that number or variable. So, for example, the postfix version of the infix expression ((5+2)(83))/4 is 5 2 + 8 3 4 /. Give an efficient algorithm, that when given an expression tree, outputs the expression in postfix notation.