Answer:
// program in C++.
#include <iostream>
using namespace std;
// main function
int main()
{
// variables
int N;
bool flag = true;
cout << "Enter a positive number: ";
// read number
cin >> N;
// check number is positive or not
while(N<0)
{
cout<<"Number is not positive!! Enter again:";
// read again if input is negative
cin>>N;
}
// check prime or not
for(int a = 2; a <= N / 2; a++)
{
if(N % a == 0)
{
flag = false;
break;
}
}
// if flag is true then prime
if (flag)
cout << "Input number is prime.";
else
cout << "Input number is not prime.";
return 0;
}
Explanation:
Read a number from user and assign it to variable "N".Check number is positive or not.If input is negative then ask again to enter a positive number until user enters a positive number.If input is divisible by any number from 2 to n/2 set flag equal to "false".After the loop, if flag is "true" then print number is prime else number is not prime.
Output:
Enter a positive number: -12
Number is not positive!! Enter again:-5
Number is not positive!! Enter again:23
Input number is prime.
