loop for adding prime numbers in c++ - c++

Question

here is a loop that is supposed to add prime numbers only and ignore non prime numbers but it is not working properly ,my skills are pretty basic , so please try to simplify your answers as much as possible,
#include <iostream>
using namespace std;
int main()
{
int n = 0, a = 0, sum = 0;
cin >> n;
for (int j = 1; j <= n; j++)
{
cin >> a;
if (a == 1)
{
continue;
}
if (a == 2 || a == 3)
{
sum += a;
}
if (a % 2 == 0)
{
continue;
}
for (int i = 3; i < a; i++)
{
if (a % i != 0)
{
sum += a;
}
else
{
continue;
}
}
}
cout << sum;
return 0;
}

Answer 1

I would prefer using this function instead. You should add cmath library:
bool isPrime(int number) {
if (number <= 1)
return false;
for (int i = 2; i <= sqrt(number); i++)
{
if (number % i == 0)
{
return false;
}
}
return true;
}
But if you want to continue with your code, after checking a == 2 || a == 3 you should continue. And last part before for loop you should define some boolean like bool isPrime = true. Then if its finds a divider you should assing it to false and break.
Your full code should be something like this:
#include <iostream>
using namespace std;
int main()
{
int n = 0, a = 0, sum = 0;
cin >> n;
for (int j = 1; j <= n; j++)
{
cin >> a;
if (a == 1)
{
continue;
}
if (a == 2 || a == 3)
{
sum += a;
continue;
}
if (a % 2 == 0)
{
continue;
}
bool isPrime = true;
for (int i = 3; i < a; i++)
{
if (a % i == 0)
{
isPrime = false;
break;
}
}
if (isPrime) {
sum += a;
}
}
cout << sum;
return 0;
}