How come '%' in my code produces another number than the one I get when calculating myself?

Question

I have my code get me the number of digits of an entered number. But if I dial it by hand I get another ...

Let's take 125 and - for example- modulate it by 10. Let's even put that in a while loop and let our number be divided by 10 each round. We get:

125%10 -> 5
12,5%10 -> 2,5
1,25%10 -> 1,25

Our sum would be 8,75. But if I use the code down below we get 8.

Does anyone know why it is that different?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EvenOrOdd
{
    class Program
    {
        static void Main(string[] args)
        {
            int num, sum = 0, r;
            Console.WriteLine("\nEnter a Number : ");
            num = int.Parse(Console.ReadLine());
            while (num != 0)
            {
                r = num % 10;
                num = num / 10;
                sum = sum + r;
            }
            Console.WriteLine("Sum of Digits of the Number : " + sum);
            Console.ReadLine();
        }
    }
}

You're parsing the numbers into an `int` which means that the numbers get rounded off. — Hans Kilian, Jun 14 '19 at 11:56
You use an integer (int) to store your result. Integers cant display decimal places so it simply saves your 8.75 as 8. Change your int up for a float and you should get your desired result with decimal places. — Niklas7, Jun 14 '19 at 11:59
@elgonzo I see it now. He enters an integer number and then try to sum the remainders. Then the first two comments applies. — Steve, Jun 14 '19 at 12:04
`Sum of Digits of the Number` Without understanding the context I would **expect** it to be 8 (1+2+5) - especially if this is homework. — mjwills, Jun 14 '19 at 12:04
@Steve, correct. Now i see it too. The code iterates over `num`, dividing it by 10 in every iteration. Doh! I need new glasses ;-) — , Jun 14 '19 at 12:05
@elgonzo 125 is being entered. The other values is what he/she is expecting to occur on each loop iteration. — mjwills, Jun 14 '19 at 12:05
As others have said, you are using integer math. Not only does it apply to the `%` modulo operation, but also to the division. If `int num = 125` then `num / 10` will evaluate to `12` (because any fraction will simply be truncated from a number in integer math) — , Jun 14 '19 at 12:08
Thank you everyone! It seems not only my datatype, but also my logic was bit off, thanks for resolving that~ @mjwills ... it's mostly about a little number game i tried programming where i need **integer** only, but i thought too far and false. — Kalex, Jun 14 '19 at 13:00

score 1 · Answer 1 · answered Jun 14 '19 at 12:09

1

You should use a floating point type, like float or double. An int cant hold the number "8.75".

Just replace int with double or float and it should work.

answered Jun 14 '19 at 12:09

JP-Hundhausen

70
1
7

Srinivasan Jayakumar · Accepted Answer · 2019-06-14T12:40:01.377

Try this code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EvenOrOdd
{
    class Program
    {
        static void Main(string[] args)
        {
            decimal num, sum = 0, r;
            Console.WriteLine("\nEnter a Number : ");
            num = int.Parse(Console.ReadLine());
            while (num >= 1)
            {
                r = num % 10;
                num = num / 10;
                sum = sum + r;
            }

            Console.WriteLine("Sum of Digits of the Number : " + sum);
            Console.ReadLine();
        }
    }
}

There are 2 issues here

-

int num, sum = 0, r; to be changed to decimal num, sum = 0, r;, this will make the decimals to be considered
This logic seems to be another issue while (num != 0), the following will be the iteration results
- Iteration1 - 125 Mod 10 = 5
- Iteration2 - 12.5 Mod 10 = 2.5
- Iteration3 - 1.25 Mod 10 = 1.25
- Iteration4 - 0.125 Mod 10 = 0.125

and goes on as 0.125 is != 0 this will continue

Thank you! You're totally right, my logic also was pretty off here, thanks for pointing that out! :) — Kalex, Jun 14 '19 at 12:56

How come '%' in my code produces another number than the one I get when calculating myself?

2 Answers2