How many 4 digit combinations can you get using numbers 0-9..?

4 answers

If zero is allowed to be a leading digit, then

10*10*10*10 if numbers can be repeated.
Yeah, I figured it's 10,000..but I'm trying to see if there are all 10,000 combinations online somewhere. I doubt it though.
you can write them down in a few hours.
start with
0000
0001
0002, and so on. Have fun.
I tried, It just confused me even more haha