negative exponent

[thatwhiteguy]

I am trying to create a function that computes a negative exponent. This is what I have, but it is not returning the proper answer. I was wondering if anyone can see where I have gone wrong. Thanks

//This function raises 1+AIR to a negative n power

float power (int num_of_pay, float number)
{
float result;
int i;
double AIR;



number = (1 + AIR);

result = 1.0;
for (i=0; i< abs (num_of_pay); i++) result *= number;
if (num_of_pay > 0)
return (result);
else
return (1.0 / result);
}

[Laharl]

AIR is not initialized, so (1+AIR) is most likely 1.

[Ganon11]

Actually, AIR is not initialized, so (AIR+1) is most likely bldsfkjdsad. It's useless, meaningless, has some random value that means nothing.

[thatwhiteguy]

Alright, now that i fixed this, I am still coming up with the same answer no matter what data I input. I need for this function to be able to perform a negative exponentiation for a monthly payment calculator.

[Laharl]

Based on the code above, you set number to one, then multiply result by it n times. Thus, nothing happens. Simply multiply result by a double cast from number n times.

[thatwhiteguy]

here is the code that I have revised to. no matter what my input it always gives me the same answer. I am not sure what I am doing wrong.

#include <iostream>

using namespace std ;
//function prototype
double payment(double balance, double AIR, int num_of_pay);
//funciton prototyp
double power (int num_of_pay, double AIR, float number);
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;

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)

/*This function computes the*/
/*amount of monthly payments*/
/*inputs???????? ???????????*/
/*balance, air, num_of_pay?*/
/*(double)?????? ???????????*/
/* outputs???????? ?????????*/
/*monthly payment???????? ??*/

{

double numerator;
double denominator;
double result;
double month_pay;

AIR = (AIR/100)/12;

numerator = balance*AIR;

denominator = (1 -result);

month_pay = (numerator/denominator);

return (month_pay);
}


//*************** *************** *************** *************** *****


/*************** *************** *************** *******/

//This function raises 1+AIR to a negative n power

double power (int num_of_pay, double AIR, float number)
{
float result;
int i;

number = (1 + AIR);

result = 1.0;
for (i=0; i< abs (num_of_pay); i++)
if (num_of_pay > 0)

return (result);
else
return (1.0 / result);
}

[Laharl]

First off, you never actually call the functions you've written.

Second, in power, you check if num_of_pay is positive, and if it is, you immediately return result. If it isn't, you immediately return 1/result. You're missing the actual multiplications that make up the power. And since result is 1, either 1 and 1/1 are 1.

[thatwhiteguy]

I see what you are saying about there being no multiplication, and so i changed the while loop to ;for (i=0; i< abs (num_of_pay); i++) result *= number;

I don not know what you mean about me not calling my functions. I was wondering if you could elaborate for me. Thank you

[thatwhiteguy]

alright, I have taken your advice, and here is the revised code. I am getting an error message. It says [Warning] in function 'double: I have no idea why it is saying this.


#include <iostream>

using namespace std ;
//function prototype
double payment(double balance, double AIR, int num_of_pay);
//funciton prototyp
double power (int num_of_pay, double AIR, float number);
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 power (int num_of_pay, double AIR, float number);
double payment(double balance, double AIR, int num_of_pay)

/*This function computes the*/
/*amount of monthly payments*/
/*inputs???????? ???????????*/
/*balance, air, num_of_pay?*/
/*(double)?????? ???????????*/
/* outputs???????? ?????????*/
/*monthly payment???????? ??*/

{

double numerator;
double denominator;
double result;
double month_pay;

AIR = (AIR/100)/12;

denominator = power (num_of_pay, AIR, number);

numerator = balance*AIR;

denominator = (1-denominator);

return (numerator/denominator);
}


//*************** *************** *************** *************** *****



//This function raises 1+AIR to a negative n power
double power (int num_of_pay, double AIR, float number)

{
float result;
int i;

number = (1 + AIR);

result = 1.0;

for (i=0; i< abs (num_of_pay); i++) result *= number;
if (num_of_pay > 0)
return (result);
else
return (1.0 / result);
}

[sicarie]

thatwhiteguy-

Just an aside, if you are going to post code, please use the code tags provided. They are on the right as you create or reply to a post, and also in our Posting Guidelines.

Thanks!