/* 
   loan.c
   by Nannette Thacker 

Loan Program:
User inserts borrowed amount, annual interest rate, monthly payment amount.
Returns monthly payment of interest, how much toward principal, balance owned on principal at end of month.

gcc loan.c -o loan.exe 

*/

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


/* prototypes */
void getvalues(float *, float *, float *); // function to get the values from the user 
void calculate(int , float *, float *, float *, float , float ); // calculate
void printhead(float, float, float);
void printsubhead(void);

int main()
{

int month ;
float interest ;
float principal ;
float balance ; // amount borrowed, entered by user
float rate ;    // interest rate
float payment ; // monthly payment
int counter ; // for number of lines to screen
int firstime ; // is this first time through loop?

getvalues(&balance, &rate, &payment); // get the values from the user
printhead(balance,rate, payment);

if(rate > 100)  // check if user input an interest rate greater than 100
{
  printf("That's highway robbery! I refuse to continue!\n\n");
  exit(0);
}
else if(rate < 1 || payment < 1)
{  printf("That is not a valid loan. Transaction aborted.\n\n");
  exit(0);
}

rate = rate / 1200 ; // get monthly interest rate 
counter = 0 ;
month = 1 ; // initialize the counter

while(balance > 0)
{

  if (counter == 0 )
    printsubhead(); // print subhead once for each screen full
  calculate(month, &interest,&principal,&balance,rate,payment);

  month ++ ;
  counter ++ ;
  if(counter >= 12)
  {  counter = 0 ;
     printf("\nPlease press any key to continue...\n");
     getchar();
     printf("\n\n\n\n\n\n\n\n");
  }
  else if(balance == 0)
    printf("\n\nThaaaaaaaaaaaaaaaaaaat's aaaaaaaallllllll folks!!\n\n\n\n");

}

return(0);

}


void printhead(float bbalance, float rrate, float ppayment)
{

printf("\n\n            TABLE OF MONTHLY PAYMENTS\n\n");
printf("Original Principal: %.2f Interest Rate %.2f percent\n\n",bbalance, rrate);
printf("          Monthly Payment Amount: %.2f\n\n",ppayment);
return ;

}

void printsubhead()
{

printf("MONTH   INTEREST   PRINCIPAL PAYMENT    BALANCE\n");

return ;

}


void calculate(int mmonth, float * iinterest, float * pprincipal, float * bbalance, float  rrate, float  ppayment)
{

// interest each month = loan balance at start of month * monthly interest rate
// principal payment each month = monthly payment amount - interest for that month
// balance each month = balance last month - principal payment this month

*iinterest = *bbalance * rrate ;
*pprincipal = ppayment - *iinterest ;
*bbalance = *bbalance - *pprincipal ;



if(*bbalance <= 0) // on final payment, don't allow balance to be less than 0
{  *pprincipal = *pprincipal + *bbalance ;
   *bbalance = 0 ;
    printf("FINAL PAYMENT OF %.2f:\n",*pprincipal + *iinterest);
}

  printf("%4d\t%6.2f\t  %10.2f\t     %10.2f\n",mmonth,*iinterest,*pprincipal,*bbalance);

// show them the first line and the error of their ways...then
if(*pprincipal < 0) // check for error in case the monthly payment is so low that nothing would go to principal
{
  printf("\n\nYou're monthly payment is TOO LOW for this INTEREST RATE! Can't continue!\n\n");
  exit(0);
}

return ;
}



void getvalues(float * bbalance, float * rrate, float * ppayment)
{

printf("\n\nPlease input the amount borrowed: ");
scanf("%f",bbalance);
printf("\nPlease input the annual interest rate: ");
scanf("%f",rrate);
printf("\nPlease input the the monthly payment amount: ");
scanf("%f",ppayment);
printf("\n\n");
getchar();


}