I don't know why I'm getting this error, this is a post fix calculator for array use review, I'll include only the push functions to save post space. If i comment out the push/pops, the errors does not occur.

The fatal errors:
Code:
error LNK2019: unresolved external symbol "public: void __thiscall stack::pop(int &)" (?pop@stack@@QAEXAAH@Z) referenced in function _main
1>client.obj : error LNK2019: unresolved external symbol "public: void __thiscall stack::push(int)" (?push@stack@@QAEXH@Z) referenced in function _main
The client program (part of)
Code:
stack myStack;
int arg1;  // this will hold the left operand.
int arg2; //this will hold the right operand.
int result; // result of every calculation, to be pushed onto stack.
int m;

int main()
{
	string s1;
	cout << "Input the numbers followed by operator(s): " << endl;
	cin >> s1;
	
	for (int i=0;s1[i]!='\0';i++) 
	{
		if (isdigit(s1[i])){  //used isdigit to check if number, if true; push.
			m = (int)s1[i];
			cout << m << endl;
		myStack.push(m); 
		}else if(s1[i]=='+'){
			myStack.pop(arg1); //pops operand off top of stack and into arg1 which is a int data
...........................................
The stack.h and stack.cpp PUSH code:

Code:
typedef int el_t;    // the el_t type is int for now
                     // el_t is unknown to the client


class stack
  { 

   private: // to be hidden from the client

        el_t     el[MAX];       // el is  an array of el_t's --int's

.........................

		void push(el_t);

......................cpp below

void stack::push(el_t n)  
{
  if (isFull())
	  throw Overflow();
  else{
	  top++;
	  el[top] = n;
  }
}