Thread: Calculation Question

So, while I think I am getting better (I THINK), one thing that will always stump me in programming are equations. More specifically, longer mathematical equations. Right now, I am making a "Loan Calculator". Basically, it just uses a switch in another function, returns the values to the main function and it prints it out.

Unfortunately, given the formula I need to use, I can't figure out how to incorporate it in into a loop, as well I can't really understand the equation, even though it explains it.. (I'm retarded when something involves complicated looking math.)

Here's my code thus far. I need to make a loop do two things::

--Loop to output for however many months entered and the information for each month (Posted guess at end of post) This isn't my major issue however.

--Figure out how exactly the equation works and use it in the loop (My major issue).
----EQUATION:: payment =.......... ........principal x rate....
.................... .... .......... 1 - ( (1+rate) to the power (-m) ) )

--I'v also got no idea what a "Principal" refers to.

Rate = annual interest rate
M = number of months

(I know it's not done but. I can't really do much unless I figure this calculation stuff out

Code:

#include <stdio.h>
#include <math.h>

int menu(void);
int swit(void);

int main(void)
{
    
    int choice;
    
    printf("1. Enter Principal\n2. Enter Annual Interest Rate\n3. Enter Duration of the loan\n4. Calculate Loan Payment\n5. Display Loan Repayment Table\n\n");
    
    choice = menu();
    
    
    printf("Month::Old Balance::Payment::Interest::Principal::New Balance");
    
    
    getchar();
    getchar();
    return 0;
}




int menu(void)
{
    int choice;
    int princ;
    int ir;
    int dur;
    int calc;
    
    printf("Make your choice from the above menu:: ");
    
    while ((choice = getchar()) != 0)
    {


    switch (choice)
    {
           
           case '1' :
                
                princ = getchar();
                break;
           case '2' :
               
                ir = getchar();
                break;
           case '3' :
                
                dur = getchar();
                break;
           case '4' :
                
                break;
           case '5' :
                
                break;
           default :
                   printf("You entered an invalid choice.\nPlease pick 1-5 or use 0 to exit the program\n");
                   break;
    }
}
    return choice;
    
}

So far my guess is going to be something like this for the loop

for (i = 1; i < months; i++). However. I am somewhat confused on how to do the calculations themselves (This is the most major thing I need help with. How exactly, after each calculation, I am supposed to re-calculate for the loop.

Any help would be greatly appreciated. I am absolutely useless when it come's to math.

Originally Posted by itsme86

Code:

for(i = 0;i < months;++i)
  principal = principal * (1 + (rate / 12));

If they input 36 for however many months they put in for time to pay, than I assume that means this can easily be altered by dividing rate / 36, rather than 12?