Variable overloading problem - please help

Hi

I have a simple program that needs to read in a decimal OR octal OR hexadecimal number, calculate the result into a decimal value and spit it out to the user. However I am little concerned as to what type can I use so the user doesn't over load my variable. when I use long double (and then getting rid of the .x portion) it gives me an ugly out put, but when I use int, or long int I am fine until I have a 20digit number as an entry and then it craps out on me.. What should I do so I can take any number for example 123456789123456789123456789 and still not lose precision

Thank you for your help

[622 byte] By [HowardAa] at [2007-9-27 7:32:18]