After:

// Calculate the simple interest on a loan
int main()
{
   // Variable declarations
   double principal, rate, interest;

   // Input the principal
   cout << "Enter the principal amount" << endl;
   cin >> principal;

   // Input the interest rate
   cout << "Enter the interest rate" << endl;
   cin >> rate;
   rate = rate / 100.0;

   // Compute the interest
   interest = principal * rate;

   // Print the interest
   cout << "The interest on $ " << principal 
        << " is $ " << interest << endl;

   return 0;
}