Question

Your program  write a program to test whether a number is prime or not.

Your program should ask user to input an integer and respond: "Prime" or "Not prime".

Don't use any library function that tests for prime numbers.

The program should continue to ask for input, till it sees a 0, when it exits.

Please submit printed pseudocodeshould ask user to input an integer and respond: "Prime" or "Not prime".

Don't use any library function that tests for prime numbers.

Thecopies of pseudocode, commented code

HOMEWORK write a program to test whether a number is prime or not. Your program should ask user to input an integer and respond: "Prime" or "Not prime". Don't use any library function that tests for prime numbers. The program should continue to ask for input, till it sees a 0, when it exits. Please submit printed pseudocode, commented code all using C++

Answer 1

Pseudo code to check if the number n is prime or not.

if n is less than or equal to 1

n is not prime

else

for i=2 to i=square root of n

if i perfectly divides n //i. e n%i==0

n is not prime

end of loop.

if none of the number divides n, then n is prime.

here is the implementation of above code

#include <iostream>
using namespace std;
// function that return true if the a number is prime, otherwise return false
bool prime(int a){
if(a<=1)// not prime
return false;
for(int i=2;i*i<=a;i++)// we only need to check from i=2 to i=sqrt(n), if any number perfectly divides a, then a is not prime
{
if(a%i==0)// a is not prime
return false;
}
// if none of the number divides a, then a is prime, so return true;
return true;
}

int main() {
   int a;// To store the input given by the user
   while(1)
   {
   cin>>a;
   if(a==0)// if the given number is 0, loop breaks
   break;
   if(prime(a))
   {
   cout<<"Prime"<<endl;
   }
   else
   cout<<"Not Prime"<<endl;
   }
   return 0;
}
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