C++ :: Program To Convert From Fahrenheit To Celsius - Linking Error?

So here is the program:

//Program to convert from Fahrenheit to Celcius
#include <iostream>

double fahrenToCelsius (double t);
//precondition:
//t is a valid tempreture in Fahrenheit
//postcondition:
//returns equivalent temp. in Celcius

[Code] .....

And here is the problem:
[Linker error] C:UsersOwnerAppDataLocalTempcckex8SZ.o:fahrenToCelsius.cpp: (.text+0x3d): undefined reference to `fahrenToCelsius(double)'
collect2: ld returned 1 exit status

I'm suspecting the program maybe that I saved it wrong? I saved it as fahrentoCelsius.cpp inside the folder "Work" ( I created this folder) which is inside the folder "Dev-cpp".