formatting - C# convert int to string with padding zeros?

In C# I have an integer value which need to be convereted to string but it needs to add zeros before:

For Example:

int i = 1;

When I convert it to string it needs to become 0001

I need to know the syntax in C#.

Answer

i.ToString().PadLeft(4, '0') - okay, but doesn't work for negative numbers
i.ToString("0000"); - explicit form
i.ToString("D4"); - short form format specifier