Question

how to make a prime number checking using c++?

Answer 1

int isprime(int n)
{
for(int i=2; i<n; i++)
{
if(n%i == 0)
return 0;
}
return 1;
}

if the return value is 1 the number-n is prime.....otherwise not

Answer 2

for( i = 3; ( i * i ) < n; i += 2 )

will speed that up.