4 LNK errors please help

I am writing this code for class, it is still in progress. I am trying to compile so I can test out the code I have so far. There is code that I temporarily turned into comments to try to fix my compile errors, but no luck. Here are the errors I come up with using Visual Studio.


main.obj : error LNK2028: unresolved token (0A00045A) "public: __thiscall Stack::Stack(void)" (??0Stack@@$$FQAE@XZ) referenced in function "public: void __thiscall Stack::listCommon(class Stack,class Stack)" (?listCommon@Stack@@$$FQAEXV1@0@Z)

1>main.obj : error LNK2028: unresolved token (0A00045B) "public: __thiscall Stack::~Stack(void)" (??1Stack@@$$FQAE@XZ) referenced in function "public: void __thiscall Stack::listDup(class Stack)" (?listDup@Stack@@$$FQAEXV1@@Z)

1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall Stack::~Stack(void)" (??1Stack@@$$FQAE@XZ) referenced in function "public: void __thiscall Stack::listDup(class Stack)" (?listDup@Stack@@$$FQAEXV1@@Z)

1>main.obj : error LNK2019: unresolved external symbol "public: __thiscall Stack::Stack(void)" (??0Stack@@$$FQAE@XZ) referenced in function "public: void __thiscall Stack::listCommon(class Stack,class Stack)" (?listCommon@Stack@@$$FQAEXV1@0@Z)

1>c:\users\mschmidt\documents\visual studio 2010\Projects\main\Debug\main.exe : fatal error LNK1120: 4 unresolved externals

Code:

#include"stack.h"
#include"collection.h"
#include<iostream>
usingnamespace std;
int main() {
  Stack a, b;
  int choice, select, add;
  for( ; ;) {
    do{
      cout << "Please choose from the following: " << endl;
      cout << "1. Add to stack" << endl;
      cout << "2. Find duplicates in stack" << endl;
      cout << "3. Find common elements between stacks A and B" << endl;
      cin >> choice;
    } while(choice < 1 || choice > 3 && choice != 4);
    if(choice == 4) break; 
      switch(choice) {
      case 1:
        cout << "Which stack would you like to add to?" << endl;
        cout << "1. Stack A" << endl;
        cout << "2. Stack B" << endl;
        cin >> select;
        if(select == 1) {
          cout << "Please enter integer to add to stack A." << endl;
          cin >> add;
          //a.insert(add);
        }
        elseif(select == 2) {
          cout << "Please enter integer to add to stack B." << endl;
          cin >> add;
          //b.insert(add);
        }
        else cout << "Invalid choice";
        break;
      case 2:
        select = 0;
        cout << "Which stack would you like to see the duplicates of?" << endl;
        cout << "1. Stack A" << endl;
        cout << "2. Stack B" << endl;
        cin >> select;
        if(select == 1) {
          a.listDup(a);
        }
        elseif(select == 2) {
          b.listDup(b);
        }
        else cout << "Invalid selection!" << endl;
        break;
      }
   }
}

Code:

#ifndef STACK_H
#define STACK_H
#include<iostream>
#include"collection.h"
class Stack : public Collection {
public:
Stack();
//Stack insert(int i);
//void remove(Stack ob1);
void listDup(Stack ob1);
void listCommon(Stack ob1, Stack ob2);
~Stack();
};
//Stack Stack::insert(int i) {
// Stack newset;
// if(length==MaxSize) {
// cout << "Set is full." << endl;
// return *this;
// }
// newset = *this;
// newset.members[newset.length] = i;
// newset.length++;
// return newset;
//}
//void Stack::remove(Stack ob1) {
// Stack newset;
// ob1.length--;
// for(int i = 0; i < ob1.length; i++) {
// newset.members[newset.length] = ob1.members[i];
// }
//}
void Stack::listDup(Stack ob1) {
  std::cout << "Here are the duplicates in the stack: { ";
  for(int i = 0; i < ob1.length; i++)
    for(int j = i+1; j < ob1.length; j++)
      if(ob1.members[i] == ob1.members[j])
        std::cout << ob1.members[i] << " }" << std::endl;
}
void Stack::listCommon(Stack ob1, Stack ob2) {
  Stack newset;
  int k = 0;
  for(int i=0; i<ob1.length; i++) {
    for(int j=0; j<ob2.length; j++) {
      if(ob1.members[i] == ob2.members[j]) {
        newset.members[k] = ob1.members[i];
        k++;
      }
    }
  }
d::cout << "The common elements of the stacks are: ";
newset.colDisplay();
}
#endif

Code:

#ifndef COLLECTION_H
#define COLLECTION_H
#include<iostream>
constint MaxSize = 100;
class Collection {

protected:
int length;
int members[MaxSize];
int find(int value);
public:
Collection() {length = 0;}
int getSize() {return length;}
void incSize() {length++;}
bool isMember(int i);
void colDisplay();
~Collection() { };
};
int Collection::find(int value) {
  for(int i=0; i<length; i++)
    if(members[i] == value) return i;
      return -1;
}
bool Collection::isMember(int i) {
  if(find(i) != -1) returntrue;
    returnfalse;
}
void Collection::colDisplay() {
  std::cout << "{ ";
  for(int i=0; i<length; i++)
    std::cout << members[i] << " ";
    std::cout << "}" << std::endl;
}
#endif
　

You told the compiler you were going to provide an implementation of a default constructor and a destructor for the Stack class. It believed you, but the linker caught you in your lie.

And it's a bad idea to put code in a header file.

Ah I did not catch that. Thank you. Can you please elaborate on not using code in headers. How would I define my class functions if it is not a good idea to use code?

You define the class in the header. You put each class's implementation in a separate C++ file, which you add to your project. All member function implementations go in their class's implementation file.

Ok I will try to do that in the future. Thank you for your help!

Note that it's bad practice to provide a constructor or destructor if your class does not require them. But if it does require a destructor then it probably requires other stuff too.
Look up and read about "The Rule of Three C++".