For PC users using Dev C++ and Projects:

Even with all 4 files in the same folders, the files may not recognize that they are supposed to interact with each other. It depends on your compiler mostly. To remedy this, specifically for Dev-C++, you must place all of the files into something called a Project. This will let the files know about each other, which is necessary.

  1. In DevC++, go to File and hover or click on New to open up the sub menu.
  2. Click on "Project..."
  3. In the new mini window that opens, you will see 5 choices for the type of project. Select Console Application.
  4. In the bottom left, give your project a name that's different from the 4 original files you downloaded, like "ElvisLovesPDEs", then hit OK.
  5. You will then be prompted to save your project. Save this project in the same folder that you saved your 4 files in.
  6. When you finish saving the project, you will notice that the program created a main.cpp file for you in DevC++. You will delete this later.
  7. See this reference picture for this part. On the left side window in DevC++, you will see your project's name with a + to it's left. Click on the + to see all files in your project. You'll notice your 4 files aren't in here. They are there in the reference picture, and that's what you'll want yours to be.
  8. To add them in, right click on your project's name, and select "Add to project". A window will open asking you for files you want to add. Search for and select the 4 files files you downloaded for this project. You may select more than 1 file to open by holding the CTRL key as you click on your files. Once all 4 are selected, hit Open.
  9. Now you should see all 4 files underneath your Project name. But now we must get rid of Main.cpp. Simply right click main.cpp and click on Remove File.
  10. Assuming you are finished coding already, you are now ready to run your project to check for errors.
  11. When you want to open these files again, you ONLY need to open up the ElvisLovesPDEs file you created. Opening up the project file will automatically give you access to all 4 of your files simply by selecting them from the left-hand side window. You should now be able to bask in the beauty of the project...