Find Prime number in C++


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Prime number program in C++

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. It means a prime number is only divisible by 1 and itself, and it start from 2. The smallest prime number is 2.

Example

#include<iostream.h>
#include<conio.h>

void main()
{
  int i,no;
  clrscr();
  cout<<"Enter any num: ";
  cin>>no;
  if(no==1)
  {
  cout<<"Smallest prime num is 2";
  }
  for(i=2;i<no;i++)
  {
  if(no%i==0)
  {
  cout<<"Not prime num";
  break;
  }
  }
 if(no==i)
 {
 cout<<"Prime num";
 }
  getch();
}

Output

Enter any num: 10
Not Prime Num

Print next Prime number

When we enter any number this code will print next Prime number.
Example: Suppose we enter 5 then next prime number is 7.

Example

#include<iostream.h>
#include<conio.h>

void main()
{
  int i,j=2,num;
  clrscr();
  cout<<"Enter any num: ";
  cin>>num;
  cout<<"Next prime num: ";
  for(i=num+1;i<3000;i++)
   {
    for(j=2;j<i;j++)
      {
     if(i %j==0)
     {
     break;
      } // if
     } // for
     if(i==j || i==1)
       {
       cout<<"\t"<<i;
    break;
    } // if
    }  // outer for
getch();
}

Output

Enter any num: 10
Next prime num 11

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