Operations on Stack values

So I'm still new to c++ after doing java for a while and really am starting to miss a lot of the things I took for granted in Java haha.  Anyways, I'm working on a linked list implementation of a stack that gets input and does a certain function to that input.  Anything that isn't a certain word or an integer is to be ignored.  Integers are to be pushed onto the stack while a plus sign ("+") for instance sums the top two nodes of the stack and replaces the 2 values with that 1 value.  Or putting the word "Empty" in the input would empty out the stack.  There are other functions, but you get the idea.  

One of the problems I'm running into now are how to do math functions on the string input. Right now, I'm trying to convert the string to an integer and back to a string but I'm unsure of how to do the last part.  Another problem is how to ignore anything that I don't need, specifically to deal with identifying integers as a part of the string input.  Attached is a part of my code.  I think if I'm able to get one of the operations to work correctly,
int Stack::Plus(){ //Add the top 2 values in the stack, remove both of the values and insert their sum
	  StackItems first;  //StackItems is a struct in my header file with typedef string StackItemType item and StackItems *below in the function
	  StackItems second;
	  first.item = topDisplay(); topDisplay gets the top item
	  int topOne = ConversiontoInt(first.item);
	  pop(); //removes top item
         int topTwo = ConversiontoInt(second.item);
	  int Sum = topOne+topTwo;
         //convert back to string here

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jkrConnect With a Mentor Commented:
In C++, you can leav3 most of the work to STL classes (http://www.sgi.com/tech/stl/), so in your case the conversion from int to string could be as simple as the attached code (also does a lot of the ignoring stuff)
#include <sstream>
string ConvertToString(const int n) {
  stringstream ss;
  ss << n;
  return ss.str();

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Well for the conversion of string to integer and vice versa, you could use:

atoi() and itoa() which perform string to integer and integer to string conversions respectively. This could help you as far as performing math operations on your string input is concerned.


int atoi(const char *str) is the definition of the atoi() function.
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