public class Product
{
    public string Name {get; set;}
    public DateTime Expiry {get; set;}
    public string[] Sizes {get; set;}
}

public void Main()
{
    Product product = new Product();
    product.Name = "Apple";
    product.Expiry = new DateTime(2008, 12, 28);
    product.Sizes = new string[] { "Small" };

    string json = JsonConvert.SerializeObject(product, Formatting.None);
    Console.WriteLine(json);
    json = JsonConvert.SerializeObject(product, Formatting.Indented);
    Console.WriteLine(json);
}