Determining variable length (number of digits) possible?

[CuriousOne]

Hello.
I'm writing a custom parser for MAX7219 - it can display data and most of ASCII characters in any digit of connected 8 digit 7 segment led display.
So say there is an input variable, XVR, which can hold any value from 1 to 9999.
I have a loop, which will extract via DIG value of individual digits from this variable and send them to MAX7219
The idea is to have loop repeat N times, where N is the total length of variable, and on each run, increase DIG value by 1, so next digit will be extracted, and in case of 2 digit variable, say from 11 to 99, it won't go thru whole display.
On ZX Spectrum we had a LEN statement, but here we not.

Any ideas?