```
current_time_str = input("What is the current time (in hours 0-23)?")
current_time_int = int(current_time_str)

wait_time_str = input("How many hours do you want to wait")
wait_time_int = int(wait_time_str)

final_time_int = current_time_int + wait_time_int
print(final_time_int)
```
If the program is run, but the user does not input a valid numerical value, the following error is generated:
```
ValueError: invalid literal for int() with base 10: '' on line 2
```
ValueErrors are not always caused by user input error, but in this program that is the case. It is worth repeating that you need to keep track of the restrictions needed for your variables, and understand what your function is expecting. You can do this by writing comments in your code, or by naming your variables in a way that reminds you of their proper form.


ValueError Example

Value errors occur when you pass a parameter to a function and the function is expecting a certain limitations on the values, and the value passed is not compatible. 

Rutgers University

Many problems in your program will lead to an error message.

Most common error messages:
- SyntaxError
- TypeError
- NameError
- ValueError

Less common error messages:
- AttributeError
- TimeLimitError
- IndexError
- IndentationError
- ExternalError
- UnboundLocalError
- ImportError
- ZeroDivisionError
- KeyError
- IOError

Error Messages

https://runestone.academy/runestone/books/published/fopp/index.html

Runestone: Foundations of Python Programming

Syntax errors happen when you make an error in the syntax of your program. Syntax errors are like making grammatical errors in writing.

Usually SyntaxErrors can be traced back to missing punctuation characters, such as parentheses, quotation marks, or commas.

SyntaxError

TypeErrors occur when you try to combine two objects that are not compatible. For example you try to add together an integer and a string. Usually type errors can be isolated to lines that are using mathematical operators, and usually the line number given by the error message is an accurate indication of the line.

TypeError

Name errors almost always mean that you have used a variable before it has a value. Often NameErrors are simply caused by typos in your code. Other times you may simply mis-remember the name of a variable or even a function you want to call.

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