Is there any way in C++ to input 6 digit number to output date (DD/MM/YY or YY/MM/DD)

I tried searching on websites but no solution

here is the question:

I input a six-digit number: 311088

Then the output should be: 31-Oct-1988

If I input 111213

Then the output should be: 13-DEC-2011 or 11-DEC-2013

If I input 121314

Then the output should be: This is not a valid date

I use only the functions from iostream and iomanip

I have no ideas to solve this question :((

Any suggestions on how to improve this program would be greatly appreciated!