First c++ file and header LNK2019 error - c++

Question

This is my first time having separate files and first time writing a header file, however I keep getting the same error I can't fix. Here are the files:
//main.cpp
#include <iostream>
#include "Bike.h"
/*
class Bike{
public:
int tyreDiameter;
int getTyreDi(){
return tyreDiameter;
}
}; */
int main(){
Bike b;
b.tyreDiameter = 50;
std::cout << b.getTyreDi();
while (1){
continue;
}
return 0;
}
//Bike.cpp
class Bike{
public:
int tyreDiameter;
int getTyreDi(void){
return tyreDiameter;
}
};
//Bike.h
#ifndef BIKE_H
#define BIKE_H
class Bike{
public:
int tyreDiameter;
int getTyreDi(void);
};
#endif
Now if I have only one file and use the class that is commented out in main.cpp everything works fine. But as soon as I try to separate the Bike class into another cpp file I get this error:
Error 1 error LNK2019: unresolved external symbol "public: int
__thiscall Bike::getTyreDi(void)" (?getTyreDi#Bike##QAEHXZ)
Error 2 error LNK1120: 1 unresolved externals
I am using Microsoft Visual Studio 2013.
Any help would be much appreciated

Answer 1

Why are you defining class Bike twice? in the cpp and in the h, the correct way would be this:
header
//Bike.h
#ifndef BIKE_H
#define BIKE_H
class Bike{
public:
int tyreDiameter;
int getTyreDi(void);
};
#endif
cpp
//Bike.cpp
#include "Bike.h"
int Bike::getTyreDi(void)
{
//implementation like return tyreDiameter;
}