# newbie question

• 07-18-2003
antheia
newbie question
This is a two part question: 1st, How do I use a negative value in an equation? I tried just putting a "-" in front of the number, but my calculations are not coming out correctly. 2nd, My error could be related to "pow"... I am using an equation for each argument, and I'm wondering if that might be what is throwing the whole thing off... Any help would be greatly appreciated!!! Thank you!! :)

okay, here's the code:
Code:

```{                 float L;                                                        //amount of loan         float R;                                                        //annual interest rate         float r = (R * 0.01) / 12;                                      //monthly interest rate         int i;                                                          //length of loan in years         double P = L * (r / 1 - pow( (1 + r), (-i * 12) ) );              //monthly payment         double total = P * (i * 12);                                    //total amount paid to bank         cout << setw(7);         cout << setiosflags(ios::fixed | ios::showpoint);         cout << setprecision(2);         cout << "\nEnter the loan amount: ";         cin >> L;         cout << "\nEnter the annual interest rate: ";         cin >> R;         cout << "\nEnter the length of the loan in years: ";         cin >> i;         cout << "\n\nLoan: \$" << L << endl;         cout << "Interest-rate: " << R << " %\n";         cout << "Years: " << i << endl;         cout << "Monthly Payment: \$" << P << endl;         cout << "\nTotal-paid: \$" << total << endl; }```
• 07-18-2003
antheia
edited original post to include code...
Thanks for checking out my question. :) I edited my first post and included the code...
• 07-18-2003
You are trying to initialise variables with other variables who's value you have not read yet, thus they maybe zero, or rubbish depending on your compiler. Instead of...
Code:

```{                 float L;                                                        //amount of loan         float R;                                                        //annual interest rate         float r = (R * 0.01) / 12;                                      //monthly interest rate         int i;                                                          //length of loan in years         double P = L * (r / 1 - pow( (1 + r), (-i * 12) ) );              //monthly payment         double total = P * (i * 12);                                    //total amount paid to bank         cout << setw(7);         cout << setiosflags(ios::fixed | ios::showpoint);         cout << setprecision(2);         cout << "\nEnter the loan amount: ";         cin >> L;         cout << "\nEnter the annual interest rate: ";         cin >> R;         cout << "\nEnter the length of the loan in years: ";         cin >> i;         cout << "\n\nLoan: \$" << L << endl;         cout << "Interest-rate: " << R << " %\n";         cout << "Years: " << i << endl;         cout << "Monthly Payment: \$" << P << endl;         cout << "\nTotal-paid: \$" << total << endl; }```
... use...
Code:

```{                 float L;                                                        //amount of loan         float R;                                                        //annual interest rate         float r;                    //monthly interest rate         int i;                                                          //length of loan in years         double P = L * (r / 1 - pow( (1 + r), (-i * 12) ) );              //monthly payment         double total = P * (i * 12);                                    //total amount paid to bank         cout << setw(7);         cout << setiosflags(ios::fixed | ios::showpoint);         cout << setprecision(2);         cout << "\nEnter the loan amount: ";         cin >> L;         cout << "\nEnter the annual interest rate: ";         cin >> R;         r = (R * 0.01) / 12;         cout << "\nEnter the length of the loan in years: ";         cin >> i;         cout << "\n\nLoan: \$" << L << endl;         cout << "Interest-rate: " << R << " %\n";         cout << "Years: " << i << endl;         cout << "Monthly Payment: \$" << P << endl;         cout << "\nTotal-paid: \$" << total << endl; }```
... for example. There are others.
• 07-18-2003
antheia
Thanks Adrian! I moved the variables r, P, and total down after the input, and the output is much better! Now I just have to figure out what I did wrong with my equation because even though the result finally shows up as a value, it's not the correct value...

here's the updated code: (I'm working on simplifying the equation)
Code:

```{         float L;                                                                //amount of loan         float R;                                                                //annual interest rate         int i;                                                                //length of loan in years         cout << setw(7);         cout << setiosflags(ios::fixed | ios::showpoint);         cout << setprecision(2);         cout << "\nEnter the loan amount: ";         cin >> L;         cout << "\nEnter the annual interest rate: ";         cin >> R;         cout << "\nEnter the length of the loan in years: ";         cin >> i;         int m = i * 12;                                                        //calculates length of loan in months         float r = (R * 0.01) / 12;                                        //calculates monthly interest rate         double P = (r / 1 - pow( ++r, -m ) ) * L;                        //calculates monthly payment            double total = P * (i * 12);                                        //calculates total amount paid to bank         cout << "\n\nLoan: \$" << L << endl;         cout << "Interest-rate: " << R << " %\n";         cout << "Years: " << i << endl;         cout << "Monthly Payment: \$" << P << endl;         cout << "\nTotal-paid: \$" << total << endl; }```
• 07-18-2003
antheia
update: it's fixed!! :D
I finally figured out what was wrong... I just broke down the equation into smaller parts. It's working great!! Thank you! :)