Question

I have just taken over some code and I see this used a lot. It seems to take the integer and create a string looking like “01”, “02” etc.

What I am not sure of is the convention used here. Why is the format {0:00} and not {00}?

string.Format("{0:00}", int.Parse(testVal) + 1);

Answer 1

The first 0 is the placeholder, means the first parameter.
00 is an actual format.

For example it could be like this:

var result = string.Format("{0:00} - {1:00}", 5, 6);

result will be 05 - 06. So the first 0 is means take the first parameter 5, while 1 means to take parameter 6.

The format is {index[,length][:formatString]}. Take a look at String.Format Method.