Installment Loan Calculator. More...

#include <math.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

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Macros
#define	FALSE 0
#define	TRUE 1

Functions
void	ABEND (int)
double	accept_i ()
double	accept_n ()
double	accept_pmt ()
double	accept_pv ()
void	accept_str (char *s)
double	calculate_i (double, double, double)
double	calculate_n (double, double, double)
double	calculate_pmt (double, double, double)
double	calculate_pv (double, double, double)
void	error_press_any_key (char *)
char *	format_currency (float)
char *	format_interest (float)
int	is_numeric (char *)
int	main (int argc, char **argv)
	iloan is a trivial application to demonstrate how a command-line program can be integrated into C-Menu Form with simple file, argument, or pipe i-o.
void	numbers (char d, char s)

Variables
int	f_i = 0
int	f_n = 0
int	f_pmt = 0
int	f_pv = 0
bool	f_quiet = false
char	in_str [BUFSIZ+1]

Detailed Description

Installment Loan Calculator.

Author: Bill Waller Copyright (c) 2025 MIT License billx.nosp@m.wall.nosp@m.er@gm.nosp@m.ail..nosp@m.com

Date: 2026-02-09

Definition in file iloan.c.

Macro Definition Documentation

◆ FALSE

#define FALSE 0

Definition at line 18 of file iloan.c.

◆ TRUE

#define TRUE 1

Definition at line 19 of file iloan.c.

Function Documentation

◆ ABEND()

void ABEND ( int e )

Definition at line 402 of file iloan.c.

                  {
    printf("ABEND: Error %d:\n", e);
    exit(EXIT_FAILURE);
}

Referenced by main().

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◆ accept_i()

double accept_i ( )

Definition at line 221 of file iloan.c.

                  {
    double i;
    while (1) {
        accept_str("Rate (annual) - - -> ");
        if (in_str[0] == '\0') {
            i = 0;
            break;
        } else {
            if (is_numeric(in_str)) {
                i = atof(in_str);
                if (i < 0)
                    error_press_any_key("interest Rate can't be less than 0");
                else
                    break;
            } else
                error_press_any_key("Interest Rate must be numeric");
        }
    }
    return (i);
}

References accept_str(), error_press_any_key(), in_str, and is_numeric().

Referenced by main().

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◆ accept_n()

double accept_n ( )

Definition at line 205 of file iloan.c.

                  {
    double n;
    while (1) {
        accept_str("Number of Payments > ");
        if (is_numeric(in_str)) {
            n = atof(in_str);
            if (n < 0)
                error_press_any_key("Number of Payments can't be less than 0");
            else
                break;
        } else
            error_press_any_key("Number of Payments must be numeric");
    }
    return (n);
}

References accept_str(), error_press_any_key(), in_str, and is_numeric().

Referenced by main().

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◆ accept_pmt()

double accept_pmt ( )

Definition at line 242 of file iloan.c.

                    {
    double pmt;
    while (1) {
        accept_str("Payment Amount  - -> ");
        if (in_str[0] == '\0') {
            pmt = 0;
            break;
        } else {
            if (is_numeric(in_str)) {
                pmt = atof(in_str);
                break;
            } else
                error_press_any_key("Payment Amount must be numeric");
        }
    }
    return (pmt);
}

References accept_str(), error_press_any_key(), in_str, and is_numeric().

Referenced by main().

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◆ accept_pv()

double accept_pv ( )

Definition at line 184 of file iloan.c.

                   {
    double pv;
    while (1) {
        accept_str("Present Value - - -> ");
        if (in_str[0] == '\0') {
            pv = 0;
            break;
        } else {
            if (is_numeric(in_str)) {
                pv = atof(in_str);
                if (pv < 0)
                    error_press_any_key("Present Value can't be less than 0");
                else
                    break;
            } else
                error_press_any_key("Present Value must be numeric");
        }
    }
    return (pv);
}

References accept_str(), error_press_any_key(), in_str, and is_numeric().

Referenced by main().

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◆ accept_str()

void accept_str ( char * s )

Definition at line 349 of file iloan.c.

                         {
    fprintf(stderr, "%s", s);
    read(0, in_str, BUFSIZ);
}

References in_str.

Referenced by accept_i(), accept_n(), accept_pmt(), and accept_pv().

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◆ calculate_i()

double calculate_i	(	double	pv,
		double	n,
		double	pmt )

Definition at line 291 of file iloan.c.

                                                    {
    double i1 = 0, i;
    double delta = 0.0000001;
    double xdelta;
    double fdelta;
    double fprimi;
    double ffact;
    double fi;
    double fman;
    double fmann;
    if (pv == 0 || n == 0 || pmt == 0)
        error_press_any_key(
            "3 non-zero values required to calculate Interest Rate");
    ffact = pv / pmt;
    xdelta = 0;
    if (ffact < n) {
        i1 = 0.0125;
        xdelta = 0.9;
    }
    while (xdelta > delta) {
        fman = 1 / (1 + i1);
        fmann = pow(fman, n);
        fi = ffact * i1 + fmann - 1;
        fprimi = ffact - n * fmann * fman;
        fdelta = fi / fprimi;
        i1 = i1 - fdelta;
        if (fdelta < 0)
            xdelta = -fdelta;
        else
            xdelta = fdelta;
    }
    i = i1 * 1200;
    if (!f_quiet)
        printf("interest Rate - - - - - -> %s\n", format_interest(i));
    return (i);
}

References error_press_any_key(), f_quiet, and format_interest().

Referenced by main().

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◆ calculate_n()

double calculate_n	(	double	pv,
		double	i,
		double	pmt )

Definition at line 279 of file iloan.c.

                                                    {
    double i1, n;
    if (pv == 0 || i == 0 || pmt == 0)
        error_press_any_key("3 non-zero values required to calculate "
                            "Number of Payments");
    i1 = i / 1200;
    n = -log(1 - pv * i1 / pmt) / log(1 + i1);
    if (!f_quiet)
        printf("Number of Payments  - - -> %s\n", format_currency(n));
    return (n);
}

References error_press_any_key(), f_quiet, and format_currency().

Referenced by main().

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◆ calculate_pmt()

double calculate_pmt	(	double	pv,
		double	n,
		double	i )

Definition at line 328 of file iloan.c.

                                                    {
    double i1, pmt;
    if (pv == 0 || n == 0 || i == 0)
        error_press_any_key(
            "3 non-zero values required to calculate Payment Amount");
    i1 = i / 1200;
    pmt = pv * i1 / (1 - pow(1 + i1, -n));
    if (!f_quiet)
        printf("Payment Amount  - - - - -> %s\n", format_currency(pmt));
    return (pmt);
}

References error_press_any_key(), f_quiet, and format_currency().

Referenced by main().

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◆ calculate_pv()

double calculate_pv	(	double	n,
		double	i,
		double	pmt )

Definition at line 266 of file iloan.c.

                                                    {
    double i1, pv;
 
    if (n == 0 || i == 0 || pmt == 0)
        error_press_any_key(
            "3 non-zero values required to calculate Present Value");
    i1 = i / 1200;
    pv = pmt * (1 - pow(1 + i1, -n)) / i1;
    if (!f_quiet)
        printf("Present Value - - - - - -> %s\n", format_currency(pv));
    return (pv);
}

References error_press_any_key(), f_quiet, and format_currency().

Referenced by main().

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◆ error_press_any_key()

void error_press_any_key ( char * s )

Definition at line 260 of file iloan.c.

                                  {
    printf("%s", s);
    getc(stdin);
    printf("\n\n");
}

Referenced by accept_i(), accept_n(), accept_pmt(), accept_pv(), calculate_i(), calculate_n(), calculate_pmt(), calculate_pv(), and main().

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◆ format_currency()

char * format_currency ( float a )

Definition at line 354 of file iloan.c.

                               {
    int digit_count, left_of_point;
    static char sstr[80];
    static char fstr[80];
    char *src_ptr, *dst_ptr, *sptr, *FPtr;
 
    sprintf(sstr, "%-18.2f", a);
    sptr = sstr;
    src_ptr = sstr;
    FPtr = fstr;
    dst_ptr = fstr;
    while (*src_ptr++ != '\0')
        ;
    src_ptr -= 2;
    left_of_point = FALSE;
    digit_count = 0;
    while (src_ptr >= sptr) {
        if (left_of_point) {
            if (*src_ptr >= '0' && *src_ptr <= '9') {
                if (digit_count == 3) {
                    *dst_ptr++ = ',';
                    digit_count = 1;
                } else
                    digit_count++;
            }
        } else if (*src_ptr == '.')
            left_of_point = TRUE;
        *dst_ptr++ = *src_ptr--;
    }
    src_ptr = dst_ptr - 1;
    dst_ptr = sptr;
    while (src_ptr >= FPtr)
        *dst_ptr++ = *src_ptr--;
    while (*--dst_ptr == ' ')
        ;
    *++dst_ptr = '\0';
    return (sptr);
}

Referenced by calculate_n(), calculate_pmt(), calculate_pv(), and main().

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◆ format_interest()

char * format_interest ( float a )

Definition at line 393 of file iloan.c.

                               {
    static char sstr[80];
    char *s;
 
    sprintf(sstr, "%-3.5f", a);
    s = sstr;
    return (s);
}

Referenced by calculate_i(), and main().

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◆ is_numeric()

int is_numeric ( char * s )

Definition at line 340 of file iloan.c.

                        {
    char c;
 
    while ((c = *s++) != '\0' && c != '\n')
        if ((c < '0' || c > '9') && c != '.' && c != ',')
            return (FALSE);
    return (TRUE);
}

Referenced by accept_i(), accept_n(), accept_pmt(), and accept_pv().

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◆ main()

int main	(	int	argc,
		char **	argv )

iloan is a trivial application to demonstrate how a command-line program can be integrated into C-Menu Form with simple file, argument, or pipe i-o.

Positional arguments: present_value The present value of the loan (the amount borrowed). number_of_payments The total number of payments to be made. interest_rate The annual interest rate (as a percentage). payment_amount The amount of each payment. The program calculates the missing value based on the three provided values. For example, if the present value, number of payments, and interest rate are provided, it will calculate the payment amount. If the present value, interest rate, and payment amount are provided, it will calculate the number of payments, and so on. The program can be used in a non-interactive way by passing the four values as arguments, with the value to be calculated set to 0. For example, to calculate the payment amount for a $10,000 loan with a 5% annual interest rate and 60 monthly payments, you could run:

iloan 10000 60 5 0

This is proof-of-concept code, and is not intended for production use. It is not designed to be robust, and does not handle all edge cases or input errors. It is intended solely to demonstrate how a simple command-line program can be integrated into C-Menu Form. In the future, more sophisticated abstractions, such as async event handlers, serialization, rpc, database, and a standardized plugin interface will be integrated into C-Menu. Feel free to modify and enhance this code as needed, but please do not use it in production without proper testing and validation. It is provided as-is without any warranty or support. Use at your own risk.

Definition at line 74 of file iloan.c.

                                {
    double pv = 0, pmt = 0, i = 0, n = 0;
    char tmp_str[BUFSIZ];
 
    signal(SIGINT, ABEND);
    signal(SIGQUIT, ABEND);
    signal(SIGHUP, ABEND);
 
    if (argc > 1 &&
        ((strcmp(argv[1], "--help") == 0 || strcmp(argv[1], "-h") == 0) ||
         argc < 4)) {
        printf("Usage: iloan [present_value number_of_payments "
               "interest_rate payment_amount]\n\n");
        exit(EXIT_SUCCESS);
    }
    if (argc > 4) {
        numbers(tmp_str, argv[1]);
        sscanf(tmp_str, "%lf", &pv);
        sscanf(argv[2], "%lf", &n);
        sscanf(argv[3], "%lf", &i);
        numbers(tmp_str, argv[4]);
        sscanf(tmp_str, "%lf", &pmt);
        if (pv != 0)
            f_pv = 1;
        if (n != 0)
            f_n = 1;
        if (i != 0)
            f_i = 1;
        if (pmt != 0)
            f_pmt = 1;
        if (f_pv + f_n + f_i + f_pmt < 3) {
            error_press_any_key(
                "Error: At least three values must be greater than zero.");
            exit(EXIT_FAILURE);
        }
        f_quiet = true;
    } else {
        if (argc != 1) {
            printf("Usage: iloan [present_value number_of_payments "
                   "interest_rate payment_amount]\n\n");
            exit(EXIT_FAILURE);
        } else {
            if (argc == 1) {
                printf("\nInstallment Loan Calculator\n\n");
                printf("Three of these values must be greater than 0.  The "
                       "field\n");
                printf("with a value of 0 will be calculated.\n\n");
                while (f_pv + f_n + f_i + f_pmt < 3) {
                    if (pv == 0) {
                        pv = accept_pv();
                        if (pv != 0)
                            f_pv = 1;
                    }
                    if (n == 0) {
                        n = accept_n();
                        if (n != 0)
                            f_n = 1;
                    }
                    if (i == 0) {
                        i = accept_i();
                        if (i != 0)
                            f_i = 1;
                    }
                    if (pmt == 0) {
                        pmt = accept_pmt();
                        if (pmt != 0)
                            f_pmt = 1;
                    }
                    if (f_pv + f_n + f_i + f_pmt < 3) {
                        error_press_any_key("Error: At least three values must "
                                            "be greater than zero.");
                    }
                }
                printf("\nYou entered:\n\n");
                if (pv != 0)
                    printf("Present Value - - - - - -> %s\n",
                           format_currency(pv));
                if (n != 0)
                    printf("Number of Payments  - - -> %s\n",
                           format_currency(n));
                if (i != 0)
                    printf("Interest Rate - - - - - -> %s\n",
                           format_interest(i));
                if (pmt != 0)
                    printf("Payment Amount  - - - - -> %s\n",
                           format_currency(pmt));
                printf("\n\nCalculation result:\n\n");
            }
        }
    }
    if (pv == 0)
        pv = calculate_pv(n, i, pmt);
    else if (n == 0)
        n = calculate_n(pv, i, pmt);
    else if (i == 0)
        i = calculate_i(pv, n, pmt);
    else if (pmt == 0)
        pmt = calculate_pmt(pv, n, i);
 
    if (f_quiet) {
        printf("%s\n", format_currency(pv));
        printf("%s\n", format_currency(n));
        printf("%s\n", format_interest(i));
        printf("%s\n", format_currency(pmt));
    }
    signal(SIGINT, SIG_DFL);
    signal(SIGQUIT, SIG_DFL);
    signal(SIGHUP, SIG_DFL);
}

References ABEND(), accept_i(), accept_n(), accept_pmt(), accept_pv(), calculate_i(), calculate_n(), calculate_pmt(), calculate_pv(), error_press_any_key(), f_i, f_n, f_pmt, f_pv, f_quiet, format_currency(), format_interest(), and numbers().

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◆ numbers()

void numbers	(	char *	d,
		char *	s )

Definition at line 407 of file iloan.c.

                               {
    while (*s != '\0') {
        if (*s == '-' || *s == '.' || (*s >= '0' && *s <= '9'))
            *d++ = *s++;
        else
            s++;
    }
    *d = '\0';
}

Referenced by main().

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Variable Documentation

◆ f_i

int f_i = 0

Definition at line 39 of file iloan.c.

Referenced by main().

◆ f_n

int f_n = 0

Definition at line 38 of file iloan.c.

Referenced by main().

◆ f_pmt

int f_pmt = 0

Definition at line 40 of file iloan.c.

Referenced by main().

◆ f_pv

int f_pv = 0

Definition at line 37 of file iloan.c.

Referenced by main().

◆ f_quiet

bool f_quiet = false

Definition at line 41 of file iloan.c.

Referenced by calculate_i(), calculate_n(), calculate_pmt(), calculate_pv(), and main().

◆ in_str

char in_str[BUFSIZ+1]

Examples: /usr/local/src/C-Menu/src/enterstr.c.

Definition at line 20 of file iloan.c.

Referenced by accept_i(), accept_n(), accept_pmt(), accept_pv(), and accept_str().

Macros

Functions

Variables

Detailed Description

Macro Definition Documentation

◆ FALSE

◆ TRUE

Function Documentation

◆ ABEND()

◆ accept_i()

◆ accept_n()

◆ accept_pmt()

◆ accept_pv()

◆ accept_str()

◆ calculate_i()

◆ calculate_n()

◆ calculate_pmt()

◆ calculate_pv()

◆ error_press_any_key()

◆ format_currency()

◆ format_interest()

◆ is_numeric()

◆ main()

◆ numbers()

Variable Documentation

◆ f_i

◆ f_n

◆ f_pmt

◆ f_pv

◆ f_quiet

◆ in_str