Write a C++ program to compute the sum of the specified number of Prime numbers

Assignment 11

              Write a C++ program to compute the sum of the specified number of Prime numbers.
(Accept the number n from user and calculate the sum of prime numbers between 1 to n)

Program Code with explanation:

1.     #include <iostream>

2.     using namespace std;

3.     int main()

4.     {

5.          int n, i, j, sum = 0, flag = 0;

6.          cout << " * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \n";

7.          cout << " \t Accept number n Accept the number n from user \n ";

8.          cout << " \t and calculate the sum of prime numbers between 1 to n \n ";

9.          cout << " * * * * * * * * * * * * * * * * * * * * * * *  * * * * * * \n \t";

10.       cin >> n;

11.       // Number 1 is not prime number,

12.       // so we start find prime numbers from 2

13.       for ( i = 2 ; i <= n ; i ++ )

14.       {

15.                   for ( j = 2 ; j <= i/2 ; j ++ )

16.                   {

17.                               if( i % j == 0)

18.                               {

19.                                           flag = 100 ;

20.                                           break ;

21.                               }

22.                   }

23.                   if ( flag == 0)

24.                               sum = sum + i;

25.                   else

26.                               flag = 0;

27.       }

28.       cout << " * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \n";

29.       cout << " \t Sum of prime numbers between 1 to " << n << " is "

30.       cout << sum << endl;

31.       cout << " * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \n";

32.       return 0;

33.  }

Explanation of Code:

Line No. 1 and 2: include the Library file and stander input – output functions.

Line No. 3: main function header.

Line No. 4 and 18: Begin and end of main function respectively.

Line No. 5: Declare the integer variables.

Line No. 7 and 10: Accept number n from user to find Factorial.

Line No. 11 and 12: Value 1 is not prime so we start to find prime numbers from value 2.

Line No. 13 and 27:

We declare the variable flag with initialization value 0. flag variable use to indicate the number is prime or not.

            First for loop is used to move from 2 to number n.

            Second for loop are used to check prime number for each iteration i.

                        In first for loop after completing each iteration of second for loop, we calculate sum using the value of flag.

For example:

 

Line No. 29 and 30: Display sum of prime numbers between 1 to n.

Line No. 32: return statement appropriate with main function return data type.

Program Code for run:

#include <iostream>

using namespace std;

int main()

{

            int n, i, j, sum = 0, flag = 0;

            cout << " * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \n";

            cout << " \t Accept number n Accept the number n from user \n ";

            cout << " \t and calculate the sum of prime numbers between 1 to n \n ";

            cout << " * * * * * * * * * * * * * * * * * * * * * * *  * * * * * * \n \t";

            cin >> n;

            // Number 1 is not prime number,

            // so we start find prime numbers from 2

            for ( i = 2 ; i <= n ; i ++ )

            {

                        for ( j = 2 ; j <= i/2 ; j ++ )

                        {

                                    if( i % j == 0)

                                    {

                                                flag = 100 ;

                                                break ;

                                    }

                        }

                        if ( flag == 0)

                                    sum = sum + i;

                        else

                                    flag = 0;

            }

            cout << " * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \n";

            cout << " \t Sum of prime numbers between 1 to " << n << " is "

cout << sum << endl;

            cout << " * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \n";

            return 0;

}

Output of Program:

            * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                        Accept number n Accept the number n from user

                        and calculate the sum of prime numbers between 1 to n

            * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 

                        100

            * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

                        Sum of prime numbers between 1 to 100 is 1060

            * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *