C# string interpolation with variable format

Question

I need to format a variable with string interpolation, and the format string is another variable:

here is my sample code:

static void Main(string[] a         


        

Answer 1

Your code is equivalent to:

Console.WriteLine(String.Format("Test 2: {0:formatString}", i));

As the formatString is in the format string, you would nest String.Format calls to put the value in the format string:

Console.WriteLine(String.Format(String.Format("Test 2: {{0:{0}}}", formatstring), i));

This isn't supported with string interpolation.