Question

A prime number is a positive integer whose positive integer divisors are 1 and the number.

E.g. 17 is a prime number

-23 is a not prime number

28 is not a prime number

-45 is not a prime number

The only even prime number is 2

Write a boolean function, isPrime that return true if its integer parameter is a prime and false if its integer parameter is not a prime number.

A simple prime number algorithm is

if n < 1 then return false

else if n = 2 then return true

else if n is an even number then return false

else

upper bound = square root(n) + 1

candidate = 3

while candidate <= upper bound and candidate does not divide n

add 2 to candidate

end while

if some condition is true

return false

else

return false

end if

end while

Write a one parameter boolean function that returns true if its parameter is a prime number and false if its parameter is not a prime number.

*Note: I need help to write out this problem in C++ while using Visual Studio 2017

Answer 1

#include <iostream>

using namespace std;

bool checkPrime(int num)
{
   int i;
   if (num <= 1) return 0;
   if (num % 2 == 0 && num > 2) return 0;
   for (i = 3; i < num / 2; i += 2)
   {
      if (num % i == 0)
         return false;
   }
   return true;
}

int main(){
   int n;
   cout<<"Enter a number: ";
   cin>>n;
   bool flag = checkPrime(n);
   if(flag == false){
      cout<<n<<" is not a prime number";
   }
   else{
      cout<<n<<" is a prime number";
   }
   return 0;
}