C# - increment number and keep zeros in front

Question

I need to make a 40 digit counter variable. It should begin as 0000000000000000000000000000000000000001
and increment to
000000000000000000000000000

Answer 1

Use the integer and format or pad the result when you convert to a string. Such as

int i = 1;
string s = i.ToString().PadLeft(40, '0');

See Jeppe Stig Nielson's answer for a formatting option that I can also never remember.