C#: Check a number is prime number or not

Last update on December 20 2024 12:52:23 (UTC/GMT +8 hours)

Write a program in C# Sharp to check whether a number is prime or not using recursion.

Visual Presentation:

Sample Solution:

C# Sharp Code:

using System;

// Class definition named 'RecExercise7'
class RecExercise7
{
    // Main method
    public static int Main()
    {
        int n1, primeNo;

        // Prompt user to input a positive number
        Console.WriteLine("\n\n Recursion : Check a number is prime number or not :");
        Console.WriteLine("--------------------------------------------------------");
        Console.Write(" Input any positive number : ");
        n1 = Convert.ToInt32(Console.ReadLine());

        // Call the function 'checkForPrime' to determine if the input number is prime
        primeNo = checkForPrime(n1, n1 / 2);

        // Output whether the number is prime or not
        if (primeNo == 1)
            Console.Write(" The number {0} is a prime number. \n\n", n1);
        else
            Console.WriteLine(" The number {0} is not a prime number. \n\n", n1);

        return 0;
    }

    // Recursive function to check for prime number
    static int checkForPrime(int n1, int i)
    {
        if (i == 1)
        {
            return 1; // Base case: If i reaches 1, it is a prime number
        }
        else
        {
            // If the number is divisible by i, it's not a prime number
            if (n1 % i == 0)
                return 0;
            else
                return checkForPrime(n1, i - 1); // Recursive call: Call checkForPrime itself with decreased i
        }
    }
}

Sample Output:

Recursion : Check a number is prime number or not :                                                          
--------------------------------------------------------                                                      
 Input any positive number : 5                                                                                
 The number 5 is a prime number.

Flowchart :

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