The main function calls two other functions

The code in the main function in Listing 2 calls two other functions:

• hello()
• goodbye()

Before - The hello function is physically defined ahead of the main function in Listing 2. 

A function prototype is not required for the main function to call the hello function.

After - The goodbye function is physically defined after of the main function in Listing 2.

Necessary to provide a function prototype to declare the goodbye function in Listing 2 in a location that is physically ahead of the definition of the main function.

Otherwise, the main function would be unable to call the goodbye function.