To write a C program for converting between Fahrenheit and Celsius, it's crucial to address several key points. The main function definition may be incorrect, and using floating-point numbers instead of integers is essential for accurate calculations. The tests for input characters 'c' and 'f' may not function as intended. Additionally, ensure that the printf statement is correctly formatted, including a semicolon at the end. It's important to avoid integer division, as using expressions like 5 / 9 will yield incorrect results; instead, use 5.0 / 9.0 to ensure floating-point division. Lastly, check that the main function has a defined return type, and clarify any issues with the compiler being used.