The user enters numbers with the last one being 0.
The program you created displays the product of all the entered numbers with the exclusion of the final 0.
The product variable starts at a value of 1 contrary to 0, which you used when calculating the sum.
When updating the product, you need to take care not to include the final 0.
You declare the product variable in type double for the result not to overflow.
using System; class Program// w w w . ja v a 2s . c o m { static void Main(string[] args) { // Preparations double product = 1; int number; // Entering numbers until zero do { // Input Console.Write("Enter a number (0 = end): "); string input = Console.ReadLine(); number = Convert.ToInt32(input); // Accumulating in intermediate product (but not the last zero!) if (number != 0) { product *= number; } } while (number != 0); // Output Console.WriteLine("Product of entered numbers (excluding zero) is: " +product.ToString("N0")); } }