Prime number generation in C++

30. C++ program to generate prime numbers up to a limit?

Note: Prime numbers will have only two factors, one factor is the number itself and the other factor is one. Ex: factors of 2 = 1, 2

Program

#include<iostream.h>

#include<stdio.h>

#include<conio.h>

void main()

            {

            int num,flag,i,j;

            clrscr();

            cout<<"Enter the limit:\n";

            cin>>num;

            if(num==1)

            {

            cout<<"No Prime numbers";

            }

            else

            {

            cout<<"Prime Numbers are: \n";

            for(i=2;i<=num;i++)

                        {

                        flag=0;

                        for(j=1;j<=i;j++)

                                    {

                                    if(i%j==0)

                                    flag++;

                                    }

                        if(flag==2)

                        cout<<i<<"\n";

                        }

            }

            getch();

            }

Output

Enter the limit:

15

Prime Numbers are:

2

3

5

7

11

13