c# check if prime number?

valentinznrByvalentinznr

I have to check in C# whether a number is a prime number.

This is the code in my program that should check this:

  if (zahl/zahl ==1 &&zahl/1 == zahl)  {    Console.WriteLine("Es handelt sich um eine Primzahl.");  } else  {    Console.WriteLine("Es handelt sich um keine Primzahl.");  }

But I would like to change it so that the number is a prime number if only the condition applies and nothing else, because otherwise everything would be a prime number.

Thanks in advance.

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FouLou
FouLou
11 months ago

What Desantrix said.

General as type:

If you can’t get paper on your own. It’ll be easy to translate into code.

What I mean is: It makes sense to know how things are going. before you get it coded.

In your example, the right way would be to look at how to find out what a prime number is.

There can help a google and give a mathematical formula. etc.

A naiver approach is simple:

If a prime number can only be divided by itself and 1. We just have to try out all the others.

We can all pay more than the number itself. Because they’re not all participable.

All negatives we can also leave because they work analogously to the positive ones. (What is divisible by 2 is also divisible by -2. etc.)

What remains are all paid from 2 to the entered zah l -1

So if we enter 5. We have to share this number by 2, 3 and 4.

Then, of course, it makes sense to know how to find out the rest of a number (Modulo bill.)

Is the rest 0. It is partable. Otherwise not.

If you have everything together. You can do that theoretically on paper.

And then you just have to convert what you do into code.

In the example stop using ner for grinding.

There are certainly more efficient methods to find out what is low. Because if we enter 72389363468234. Then we have to do so many calculations. Until we have results, and that may take a little bit.

0
KBM2307
KBM2307
11 months ago

If you share a variable with exactly the same variable, you will get the value 1.

Therefore, your program will always claim it would be a prime number, even with numbers that are not prime numbers.

0
Valentin1720653
Valentin1720653
11 months ago

A prime number is a number that can only be divided by one and oneself…

I certainly don’t write the code now, but so much is said, you need a for loop for testing a prime number n running <=n. During each run, you will test whether the % operator (Modulo) will remain a remainder in the division.

If this is only the case with 1 and the number n itself, this is a prime number. Otherwise not.

1
cleanercode
cleanercode
11 months ago

Do not accept liability.

namespace PrimePower
{
    internal class Program
    {
        private static bool isDividable(int number)
        {
            for (int i = 2; i < number; i++)
                if (number % i == 0)
                    return false;

            return true;
        }

        private static bool isPrime(int number)
        {
            return (isDividable(number) || number == 2 );
        }

        static void Main(string[] args)
        {
            Console.WriteLine(isPrime(7));
        }
    }
}

But I leave this case to you:)

number == 1

Fun 🙂

0
Maxi170703
Maxi170703
11 months ago

Number/number is always 1 and number/1 is also always number. So you’re not checking anything. Number/number will be issued for number = 0

1