K&R Exercise 4-6 Problem thinking of a solution.

Question

In k&r we have managed to create an RPN.

The exercise now is to:

Add commands for handling variables, (It's easy to provide twenty-six variables with single letter names.) Add a variable for the most recently printed value.

So this is meant to act somewhat like the Python interpreter, where we can do:

>>>5
>>>_ (where _ prints 5)
>>>_ + 5 (which prints 10)

or A = 5 _ + A (which prints 10)

and so on, but I'm not so sure about how I want to go about it in C, I just feel stumped, the RPN as is, is shown here: http://omploader.org/vNHZvYQ

Please help :)

Answer 1

Create a 26th variable. Any time you print something, write that value into the 26th variable. When they use _ (or whatever name you choose) read from that variable.

Answer 2

This is first step of building a command line calculator i guess.

Parse the input string for operands and operator. Map the operator to a enum

enum operator { TYPE_ADD, TYPE_SUBTRACT,TYPE_MAX);

Call function to compute result

  int    calculate(int i_op1, int i_op2, operator e_operator)
           {
              /*Use switch case to calculate result*/
           }

Save this result into a variable. In input in the string is equal to "_" then use this as first input to the funtion calculate.