+ } else if expr == "?" || expr == "h" || expr == "H" {
+ // display help text
+ println! ("Type an expression in postfix style to evaluate.");
+ println! ("Example: 4 5 + 12 -");
+ println! ("Supported operators: +, -, *, /");
+ println! ("Type q, Q to quit");
+ continue;
+ } else if expr == "" {
+ // continue without proceeding
+ continue;