I tried about a dozen numbers with your program and they all came up with the correct responses.
Just a comment or two:
You might want to add a space after each digit name: e.g. "nine " instead of "nine"
The variable right_digit is "set but never used" according to my compiler. It can be deleted. You should turn on all error messages and warnings from your compiler.
The variable left_digit is used only briefly and can also be deleted if you replace
left_digit = originalnumber/n;
switch (originalnumber / n)
Case zero should have its own case -- use default to catch an unexpected / error case.
Nice program overall.