Re: C++ Primer ex 9.34, using a Stack

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 19 Oct 2007 08:19:58 GMT

Message-ID:

<OMZRi.11693$ZA.7588@newsb.telia.net>

On 2007-10-19 08:35, cront wrote:

All I was able to come up with is this code. I am get confused on how to
solve this problem provided a very small amount of Stack operations.

/* C++ Primer - 4/e
*
* Exercise 9.42
* STATEMENT
* Use a stack to process parenthesized expressions. When you see an
open parenthesis, note that it was seen. When you see a close
parenthesis after an open parenthesis, pop elements down to and
including the open parenthesis off the stack. push a value onto the
stack to indicate that a parenthesized expression was replaced.

The easiest way to note that an opening parenthesis was seen is to push
is onto the stack. Then when you read in a closing parenthesis you start
poping until you find an opening one.

The below code will replace all parenthesised expressions with 5 (even
nested parentheses (I wrote it really quick, so it might contain bugs).

#include <iostream>
#include <stack>

int main()
{
  std::stack<char> stack;

  char c;
  while ( std::cin >> c )
  {
    if ( c != ')' )
      stack.push(c);

    else
    {
      char p;
      do {
        p = stack.top();
        stack.pop();
      } while ( p != '(' );

      stack.push('5');
    }
  }

  while ( !stack.empty() )
  {
    std::cout << stack.top() << "\n";
    stack.pop();
  }
}

--
Erik Wikstr??m