How to multiple all digits of x number?

Question

I'm doing a counting program and i need to multiple all digits of x number by it self.

for example: number 123456789;

1*2*3*4*5*6*7*8*9=362,880

Answer 1

A good solution is provided in the comments, but it isn't very easy to follow if you are trying to figure out what you are actually doing. The following code is a bit more verbose, but shows you what is actually happening each step of the way:

using System;

class MainClass {
  public static void Main () {
    int myNumber = 123456789;  //store original number
    int newNumber = (int)Math.Abs(myNumber);  //changes the number to positive if it is negative to prevent string formatting errors.
    int product = 1; //store product start point
    string myString = newNumber.ToString(); //convert number to string

    foreach(char number in myString){  //loop through string
      string numberString = number.ToString();  //convert chars to strings to ensure proper output
      int oneDigit = Convert.ToInt32(numberString); //convert strings to integers
      product = product*oneDigit;  //multiply each integer by the product and set that as the new product
    }
    if(myNumber < 0){product = -product;} 
    //if the number is negative, the result will be negative, since it is a negative followed by a bunch of positives.
    //If you want your result to reflect that, add the above line to account for negative numbers.
    Console.WriteLine(product);  //display product
  }
}

Output>>> 362880  //The output that was printed.

So we start by converting our number into a string so we can iterate through it. Then we have a foreach loop that goes through each character in the string, converts it into an integer, and multiplies it by the product of the previous numbers. Each time a new multiplication is performed, the product is updated, until, when you reach the end of the number, you have the product of all digits. This is a good project to become familiar with looping. I would recommend playing around with variations of it such as multiplying each number by the original number, multiplying together only multiples of 3, only multiplying numbers less than 5, or only multiplying the first 5 numbers to get a better handle on what's happening in a loop.