trying to code a incremental number generator

[DataCom]

Hi,
I am new at php and I am trying to code a incremental number generator. I want to be able to modify it if needed. The numbers would look like ex: daf0001 or whatever letters I want to use at the beginning. It would really be nice to be able to have it start at a then go to z for the beginning numbers and change to the next letter as needed. I also want to be able to control the length of the digits. ex 8 or 10.
Is there code anywhere simular to this available?
If not, how do I code this to work? The code would need to be able to display the number and it can't regenerate a new number thats already in use. So It will need to have some sort of checking system to prevent that from happenning.

I have searched google multiple times on this but keep getting results related to random number generation.

any help would be greatly appreciated.

Thanks,
DataCom

[barand]

for ($i='aa'; $i < 'cc'; $i++) {
	for ($j=0; $j < 100; $j++) {
		printf ('%2s%02d<br/>', $i, $j);
	}
}

[DataCom]

Thanks Barand!

Now if I want to keep the letters the same and only increment the numbers, how can I do that?
I also want it to output 1 number at a time using a button when needed.
is this possible?
If I understand this correctly it would always generate the same combinations but but being used 1 number at a time there is no way at this time for it to pick up from the last number used. It would be great for creating the initial generated numbers. What this is going to be used for is number system used on a home town classifyed adds. the purpose of the numbers is to give each user making a classifyed add a number for the add in the add creation page so they input the number so thier add is searchable by that number. So I want to use a button on the add creation page so it displayes the next number not is use by the system.
if it was using mysql to store the generated numbers then it would just need to pull them one at a time incramentaly as needed.

Thanks,
DataCom