Marks Mortgage Calculator Program Execution Error

Hi! Lately,
I have been experiencing run time errors during program execution. For example, I have serious mathematical errors that do not add up, a division by zero, invalid user input and obvious resource in/output issues like the file is missing.
How can I resolve this problem?

Error:
Marks Mortgage Calculator
Unhandled exception has occurred in your application. If you click Continue, the application will ignore this error and attempt to continue.
If you click Quit,the application will close immediately.
Attempted to divide by zero.
Details Continue Quit
