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C# Program to Display Prime Numbers between Given Interval

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Prime number

C# program to display prime numbers between given interval has been shown here. For example, the prime numbers between 10 and 20 are 11, 13, 17, 19. In this program, the upper and lower bounds of the interval are taken as inputs.







1. Algorithm to Display Prime Numbers between Given Interval


1. Take lower bound l and upper bound u as inputs.

2. For each number from l to u, check if it is a prime number.

3. If a number is prime, add it to a list of prime numbers.

4. Display the list after all the numbers within the interval have been checked.




2. Pseudocode to Display Prime Numbers between Given Interval


Input : Lower bound $l$ and Upper bound $u$

Output : Prime numbers between $l$ and $u$

1. Procedure primesBetweenInterval($l, u$):

2. Repeat for $n \in [l, u]$:

3. $flag \leftarrow 0$

4. Repeat for $i \in [2, \sqrt{n}]$:

5. If $n \mod i$ = 0:

6. $flag \leftarrow 1$

7. break

8. If $flag = 0$:

9. Print "$n$ is a prime"

10. End Procedure





3. Time complexity to Display Prime Numbers between Given Interval


Time Complexity: O($n\sqrt{n}$)

Here, $n$ is the number of elements between $l$ and $u$ inclusive




4. C# Program & output to Display Prime Numbers between Given Interval

Code has been copied
/********************************
     alphabetacoder.com
C# program to display prime 
numbers between given intervals
*********************************/

using System;

namespace AverageSum {
    class Program {
        // function to check prime
        static bool check_prime(int num) {
            // declare variables
            int i;
            // no prime number less than 2, so return false
            if (num < 2)
                return false;
            // check divisibility of num
            for (i = 2; i <= Math.Sqrt(num); i++) {
                if (num % i == 0) {
                    return false; // num is composite so return false
                }
            }
            // num is prime so return true
            return true;
        }

        static void Main() {
            // declare variables
            int n1, n2, i;

            // take input of the inteval
            Console.Write("Enter the lower bound of interval = ");
            n1 = Convert.ToInt32(Console.ReadLine());
            Console.Write("Enter the upper bound of interval = ");
            n2 = Convert.ToInt32(Console.ReadLine());

            Console.Write("Prime numbers between " + n1 + " and " + n2 + ": ");
            // find primes between n1 and n2
            for (i = n1; i <= n2; i++) {
                // check if current number is prime
                if (check_prime(i)) {
                    Console.Write(i + " ");
                }
            }

            // wait for user to press any key
            Console.ReadKey();
        }
    }
}

Output

Enter the lower bound of interval = 10

Enter the upper bound of interval = 200

Prime numbers between 10 and 200: 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199





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