string name = "Bill";
var birthday = new DateTime(1955, 10, 28);

// Formatted string C# 5:
Console.WriteLine("Hello, {0}! you born a {1}.", name,  birthday.DayOfWeek);

// String interpolated C# 6:
Console.WriteLine($"Hello, {name}! you born a {birthday.DayOfWeek}.");

// Result:
// Hello, Bill! you born a Friday.
// Hello, Bill! you born a Friday.