Help with scanners

Hi! I am a student, in my first C++ class. I am trying to program a scanner that would take a string of non-numeric numbers postfix, convert to numeric numbers and give a value. I've exhausted all my resources and just can't figure out where my program is going wrong. Any suggestions would be greatly appreciated! This is my first time posting here, so I hope that I did this right. Thank you

No matter what string I enter (like "100 25 +"), I only get a value of 0. I think my problem is in my "int convert (char*)" function but I'm not sure.

Code:

---


#include <iostream.h>
#include <math.h>

#define E 0
#define L 1
#define G 2
#define C -1

int strcomp (char*, char*);
int eval (char*);
int scanner (char*, int, char*);
int convert (char*);

class stack
{
  public:
  int *arr;
  int ptr;
  int n;
  stack (int n);
  ~stack ();
  int push (int value);
  int pop ();
  int empty ();
  int full ();
};

stack::stack (int value)
{
  n = value;
  arr = new int [n];
  ptr = 0;
}

stack::~stack ()
{
  delete []arr;
}

int stack::push (int value)
{
  if (ptr < n)
  {
      arr [ptr] = value;
      ptr++;
      return E;
  }
  else return L;
}

int stack::pop ()
{
  ptr--;
  return arr [ptr];
}

int stack::empty ()
{
  if (ptr == 0) return E;
  else return L;
}

int stack::full ()
{
  if (ptr == n) return E;
  else return L;
}

int main ()
{
  int n;
  char arr [100];
  cin.getline (arr, 100);
  while ( strcomp(arr, "quit") != E)
  {
      n = eval (arr);
      cout << "The value of " << arr << " = " << n << endl;
      cin.getline (arr, 100);
  }
}

int strcomp (char*str1, char*str2)         
{                                                           
  int k = 0;
  while (str1 [k] == str2 [k])
  {
      if (str1 [k]  == '\0') return E;
      else k++;
  }
  if (str1 [k] < str2 [k]) return L;
  else return G;
}

int eval (char*str)
{
  int pos = 0, value;
  char token [100];
  stack stk1 (100);
  while (pos != C)
  {
      pos = scanner (str, pos, token);
      char fchar = token[0];
      if (fchar == '+' || fchar == '-' || fchar == '*' || fchar == '/')
      {
        int opr1 = stk1.pop ();
        int opr2 = stk1.pop ();
        if (fchar == '+') value = opr1 + opr2;
        if (fchar == '-') value = opr1 + opr2;
        if (fchar == '*') value = opr1 + opr2;
        if (fchar == '/') value = opr1 + opr2;
        int rel = stk1.push (value);
      }
      else 
      {
          int num = convert (token);
          int ret = stk1.push (num);
      }
  }
  return stk1.arr [0];
}

int scanner (char*str, int str, char*token);
{
  int i = st;
  while (str [i] != ' ')
  {
      if (str [i] == '\0') return C;
      else
      {
        token [i-st] = str [i];
        i++;
      }
  }
  token [i-st] = '\0';
  i++;
  return i;
}

int convert (char*str)
{
  int i = 1;
  int num;
  num = str [i] - '0';
  while (str [i] != '\0')
  {
      num = num * 10;
      num = num + str [i] - '0';
      i++;
  }
  return '\0';
}

---