This is what has been annoying me just a bit and would appreciate any help. I have to write this program that encrypts and decrypts 4 character numbers.
For example..
Encrypt 3246 by adding 7 to each digit and modulus that total by 10.
(x+7) % 10
(3+7) % 10 = 0
(2+7) % 10 = 9
(4+7) % 10 = 1
(6+7) % 10 = 3
Now that was the easy part now I have to decrypt 0913 so I get the value 3246.
I tried to find the opposite calculation of modulus but to no avail. I would appreciate any help.