C# convert int to string with padding zeros?

Question

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

Answer 1

public static string ToLeadZeros(this int strNum, int num)
{
    var str = strNum.ToString();
    return str.PadLeft(str.Length + num, '0');
}

// var i = 1;
// string num = i.ToLeadZeros(5);