Best method of string validation?

[daynorb]

In your opinion, what is the best method for validating a user input string.
For example , to make sure that the user input 7 digits as opposed to letters or a mix of the two.

Should I use a loop to check isdigit() for each character, or is there a way to look at the string as a whole?

What would this kind of structure look like?

Regards,
Braydon

[laserlight]

to make sure that the user input 7 digits (...) Should I use a loop to check isdigit() for each character

That sounds like a good solution, assuming that you also check that exactly 7 digits were entered. Is it the best? Maybe, maybe not (e.g., if a regular expression library were available, maybe using that would be better, or it might be overkill).