C#Program to find prime numbers in a given range

C#Program to find prime numbers in a given range – Learn how to identify the prime number, and display prime numbers between the given rane.

Prime Number

A number which is divisible by 1 and itself is called prime number. Prime number contains only 2 factors i.e 1 and the self number.

For example, consider the number 7, for this number 1, 7 are the factors.7 is not disvisible by any other number.

Here are the first few prime numbers 2,3,5,7,11,13…

All the above numbers are divisible by 1 and the self numbers.

NOTE

2 is the even prime and remaining all prime numbers  are odd numbers

C#Program to find prime numbers in a given range

Example program for generating prime numbers

Method -1  : Mathematical Approach – using  k iterations 

 class Program
    {
        static void Main(string[] args)
        {
            int num1=3,num2=13;
            Boolean flag = true; ;

            Console.WriteLine("Prime numbers between "
            +num1 +" and " + num2);
            for (int k = num1; k <= num2; k++)
            {   
             //  loop the iterations for k times
                for (int i = 2; i <k; i++)
                {
                    if ((k % i) == 0)
                    {
                        flag = false;
                        break;
                    }
                }
                if (flag == true)
                {
                    Console.WriteLine(k );
                }
                flag = true;
            }
        }
    }

output

Prime numbers between 3 and 13
3
5
7
11
13

Method -2  using k/2 iterations.

 class Program
    {
        static void Main(string[] args)
        {
            int num1=3,num2=13;
            Boolean flag = true; ;

            Console.WriteLine("Prime numbers between "
             +num1 +" and " + num2);
            for (int k = num1; k <= num2; k++)
            {
               //loop the iterations for k/2 times
                for (int i = 2; i <=k/2; i++)
                {
                    if ((k % i) == 0)
                    {
                        flag = false;
                        break;
                    }
                }
                if (flag == true)
                {
                    Console.WriteLine(k );
                }
                flag = true;
            }
        }
    }
}

Method -3  using square root function

class Program
    {
        static void Main(string[] args)
        {
            int num1=3,num2=13;
            Boolean flag = true; ;

            Console.WriteLine("Prime numbers between "
             +num1 +" and " + num2);
            for (int k = num1; k <= num2; k++)
            {
               // loop the iterations for sqrt(k) times
                for (int i = 2; i <=(int)Math.Sqrt(k); i++)
                {
                    if ((k % i) == 0)
                    {
                        flag = false;
                        break;
                    }
                }
                if (flag == true)
                {
                    Console.WriteLine(k );
                }
                flag = true;
            }
        }
    }