To process the postfix string and break it into operators/operands, you may find it useful to use the standard library class stringstream to process postfix. You can create an object of the stringstream class from a C++ string, and then use the same operators and member functions to read input from the stringstream that you can use with any other input stream (such as cin or an input file stream variable).

If you do use the stringstream class, your code for evaluate() will look something like this:

#include

#include

...

using std::string;

using std::stringstream;

...

int evaluate(const string& postfix)

{

string op;

stringstream ss(postfix); // Create a stringstream object from the postfix string.

// You can now read from the stringstream as if it were standard input. The end of the

// string will be treated as the end of input.

while (ss >> op)

{

// op is a C++ string containing the next operator/operand in the postfix expression.

...

}

...

}

Postfix evaluation algorithm

Here is a description of the logic for evaluating a postfix expression using a stack.

• Let eval_stack be a stack used to hold operands during evaluation.
• Let postfix be a string containing the postfix expression tokens.