Invisible wrote:

> #include <iostream>
> #include <vector>
> #include <string>
> 
> using namespace std;
> 
> bool StackCheck(vector<int> stack, int min)
> {
>   if (stack.size() >= min) return true;
> 
>   cout << "Stack underflow." << endl;
>   return false;
> }
> 
> void Add(vector<int>& stack)
> {
>   if (!StackCheck(stack, 2)) return;
> 
>   int x = stack.back(); stack.pop_back();
>   int y = stack.back(); stack.pop_back();
>   stack.push_back(x + y);
> }
> 
> void Sub(vector<int>& stack)
> {
>   if (!StackCheck(stack, 2)) return;
> 
>   int x = stack.back(); stack.pop_back();
>   int y = stack.back(); stack.pop_back();
>   stack.push_back(x - y);
> }
> 
> int main()
> {
>   cout << "Calc #01" << endl;
> 
>   vector<int> stack;
>   string cmd;
> 
>   while (true)
>   {
>     for (int i=0; i<stack.size(); i++)
>     cout << "[" << i << "]: " << stack[i] << endl;
> 
>     cout << "Calc> ";
>     cin  >> cmd;
> 
>     if (cmd == "^") break;
>     if (cmd == "+") {Add(stack); continue;}
>     if (cmd == "-") {Sub(stack); continue;}
>     stack.push_back(1);
>   }
> 
>   cout << "Exit." << endl;
> }

module Main (main) where

main = do
   putStrLn "Calc #01"
   main_loop []

main_loop stack = do
   mapM_ (\(n,v) -> putStrLn $ "[" ++ show n ++ "]: " ++ show v) (zip 
[0..] stack)

   putStr "Calc> "
   cmd <- getLine

   case cmd of
     "^" -> return ()
     "+" -> binary (+) stack
     "-" -> binary (-) stack
     _   -> main_loop (1:stack)

binary fn stack = case stack of
   x:y:zs -> do main_loop ((fn x y) : zs)
   _      -> do putStrLn "Stack underflow."; main_loop stack


Somehow... it seems so much easier in Haskell. ;-)

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