Today we shall learn how to write a program to find a number is Prime number or not.Before we start writing a program we should learn the basic definition.A number is said to be prime number if”It is divisible by one and itself only”.Therefore while deciding a prime number we should about the factors of the given number.

To find the factors of the given number we should divide the number.If the remainder is 0 then number is divisible and it is said to be the factor of the given number.Here we shall use the modulous operator(%) to find the remainder.Let us write the code:

#include<iostream.h>
#include<conio.h>
class prime_number
{
  public:
  int n;
  void calculating();
};
void prime_number :: calculating()
{

    int flag=0,count=0;
    for(int i=2;i<n;i++)
     {
       count=0;
       if(n%i==0)
       {
	 count++;
	 flag++;
       }
       if(count !=0)
	cout<<"\nGiven number is divisible by"<<i;
     }
    if(flag ==0)
     cout<<"\n******Given number "<<n<<" is a prime number*******";
    else
    cout<<"\n********There fore given number "<<n<<" is not a prime number*********";
}
void main()
{
  clrscr();
  prime_number ob;
  cout<<"Enter the number to check for prime number:";
  cin>>ob.n;
  ob.calculating();
  getch();
}

Output:

You can download the code:download