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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Can this program be improved?
Date: Sat, 25 Dec 2021 11:22:32 -0800
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Xref: csiph.com comp.lang.c:164067

Manu Raju <MR@invalid.invalid> writes:

[revised to repair spacing issues]

> #include <stdio.h>
> #include <stdlib.h>
> #include <math.h>
>
> int main()
> {
>     float P = 100000; // Loan Amount
>     float r = 7.5; // Advertised Interest Rate
>     int n = 12; // Loan Period
>     float payBack = (P * r / 1200 * pow(1 + r / 1200, n))
>         / (pow((1 + r / 1200), n) - 1);
>     float Opening = P; // Opening Balance
>     float closing = 0; // Closing Balance
>     float interest = 0;
>     float Total = 0;
>     float repaid = 0;
>     
>     printf("\nMonthly payment is: %.2f\n", payBack);
>
>     printf("%10s %14s %13s %10s %14s %12s\n", "Month", "Beginning",
>         "Interest", "Total", "Repayment", "Balance");
>
>     for (int i = 1; i <= n; i++)
>     {
>         for (int j = 0; j <= n; j++)
>         {
>             interest = Opening * r / 1200;
>             Total = Opening + interest;
>             repaid = payBack;
>             closing = Total - payBack;
>         }
>         printf("%10d %14.0f %13.0f %10.0f %14.0f %12.0f\n", i,
>             Opening, interest, Total, repaid, closing);
>         Opening = closing;
>     }
>     return 0;
> }

I gave some other comments in another response.  Here is
a re-writing to make my suggestions more concrete.

(Note to all:  Merry Christmas!)


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

static  void    show_payment_table( double, double, int );

int
main(void){
    show_payment_table( 100000, 7.5, 12 );
    return  0;
}

void
show_payment_table( double amount, double yearly_percentage_rate, int months ){
    double const  monthly_rate  = yearly_percentage_rate / 100 / 12;
    double const  compounded    = pow( 1 + monthly_rate, months );
    double const  adjustment    = compounded / (compounded - 1);
    double const  payment       = amount * monthly_rate * adjustment;

    double balance = amount;

    printf( "\nMonthly payment is: %.2f\n", payment );

    printf( "%10s %14s %13s %10s %14s %12s\n",
        "Month", "Beginning", "Interest", "Total", "Repayment", "Balance"
    );

    for(  int i = 1;  i <= months;  i++  ){
        double const  interest  = balance * monthly_rate;
        double const  owing     = balance + interest;
        double const  remaining = owing - payment;

        printf( "%10d %14.0f %13.0f %10.0f %14.0f %12.0f\n",
            i, balance, interest, owing, payment, remaining
        );
        balance = remaining;
    }
}