C#: To check a number is prime or not

Last update on August 25 2025 12:47:18 (UTC/GMT +8 hours)

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

Visual Presentation:

C# Sharp Exercises: Function : To check a number is prime or not

Sample Solution:

C# Sharp Code:

using System;

// Class definition named 'funcexer9'
public class funcexer9
{
    // Method to check if a number is prime or not
    public static bool chkprime(int num)
    {
        // Loop to check for factors of the number
        for (int i = 2; i < num; i++)
        {
            if (num % i == 0)
            {
                return false; // If any factor found, the number is not prime, return false
            }
        }
        return true; // If no factors found, the number is prime, return true
    }

    // Main method, the entry point of the program
    public static void Main()
    {
        // Display a description of the program
        Console.Write("\n\nFunction : To check a number is prime or not :\n");
        Console.Write("--------------------------------------------------\n");

        // Prompt the user to input a number
        Console.Write("Input a number : ");
        int n = Convert.ToInt32(Console.ReadLine());

        // Check if the number is prime using the 'chkprime' method
        if (chkprime(n))
        {
            Console.WriteLine(n + " is a prime number"); // Display if the number is prime
        }
        else
        {
            Console.WriteLine(n + " is not a prime number"); // Display if the number is not prime
        }
    }
}

Sample Output:

Function : To check a number is prime or not :                                                                
--------------------------------------------------                                                            
Input a number : 23                                                                                           
23 is a prime number

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