15. Program that inputs an integer and displays whether it is a prime number or not.

Chapter 6: 

Looping Structures

Programming Exercise

Problem # 15:

Write a program that inputs an integer and displays whether it is a prime number or not.

Solution:

#include<iostream>
#include<conio.h>
using namespace std;
int main()
{
    int c, n, p;
    cout<<"Enter a number: ";
    cin>>n;
    if(n>1)  
        p=1;
    else
        p=0;
    for(c=2;c<n;c++)
    {
        if(n%c==0)
        {
            p=0;
            break;
        }
    }
    if(p==1)
    cout<<endl<<n<<" is a prime number.";
    else
    cout<<endl<<n<<" is a composite number.";  
    return 0;
}

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17. Program that continuously inputs positive integer values from the user. The program should finally display the second largest number entered.