incorrect answer

[thatwhiteguy]

I have been working on this program for a few days now, and I am at a loss as to what is wrong. I am new to c++, so I am sure that it must be something simple that I am missing, but I can not pin point it. Below is my code, and no matter what I input it gives me the same answer: $1.#INF. All I need for it to do is calculate the monthly payments .

#include <iostream>
 
using namespace std ;
//function prototype
double payment(double balance, double AIR, int num_of_pay);
//funciton prototype
double power (int num_of_pay, double AIR);
int main ()
{
  double month_pay; //
  double balance; //amount of loan
  double AIR; //annual interest rate
  int num_of_pay ; //number of payments over course of loan
  double result;
 
  cout<< "Welcome to the loan payment calculator program!"<<endl ;
 
  cout<< " Please enter the loan amount:"<<endl ;
  cin>> balance;
 
   cout<< " Please enter the annual interest rate as a percentage, not a decimal:"<<endl; 
   cin>> AIR;
 
   cout<< "Please enter number of payments you will pay:"<<endl;
   cin>> num_of_pay;
   month_pay = payment(balance, AIR, num_of_pay);
   cout<< "The amount of your monthly payment is:  $" << month_pay <<endl;
 
   system("PAUSE");
   return (0);
}
 
double payment(double balance, double AIR, int num_of_pay)
{
 
    double month_pay;
 
   AIR = (AIR/100.00)/12.00;
 
   month_pay = (balance * AIR) / ( 1.0 - power ((! + AIR), -num_of_pay));
 
   return (month_pay);
}
 
 
double power (int num_of_pay, double AIR)
{
    double result;
    int i;
 
    result = 1.0;
    for (i=0; i< abs (num_of_pay); i++) result *= (1 + AIR );
 
    if (num_of_pay > 0)
        return (result);
    else
        return (1.0 / result);
}

[mschenkelberg]

what do you pass to the program?

[thatwhiteguy]

what do you pass to the program?

I pass the amount of the loan. We'll say 5700. The amount of interest, we'll say 12 . And the amount of total payments, we'll say 36.

[weaknessforcats]

month_pay = (balance * AIR) / ( 1.0 - power ((! + AIR), -num_of_pay));

So, what's the ! for ??? .....................................^