Padding integer with zeros

Question

I know I can format string with left padding with spaces with line:

int i=5;
serial = String.Format("{0,20}", i);

But how to left pad wit 0 in order to get string below?

00000000000000000005

Always 20 zeros? Or always 2 characters? – Austin T French Oct 10 '18 at 18:14 — Austin T French, Oct 10 '18 at 18:14

score 2 · Accepted Answer · answered Oct 10 '18 at 18:13

You can use the built-in function PadLeft:

int i = 5;
var result = i.ToString().PadLeft(8, '0');

Note: this doesn't work for negative numbers (you'd get 00000000-5).

For that you can use the built-in formatters:

int i = 5;
var result = string.Format("{0:D8}", i);

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