C Programming

April 10th, 2019

Contact Lens Calculations

By the end of 1992 MS-DOS was in its last days of glory. I had begun writing programs with C and compiling them with MS-Quick C.

I knew an optometrist in the Sumter, SC computer club. He had a 'BASIC' program that I converted to an executable C program.

Below are two screen shots of the program running in DOSBox. Old MS-DOS programs will run on new computers using this virtual MS-DOS.

Install DOSBox and check out eye10.exe. And if you really want to have fun, download the source code make some alterations and compile it.

/* Original program written in "BASIC"      */
/* by D. B. Grimland LCDR USN ON 11 DEC 87. */
/*                                          */
/* Converted to the "C" language Dec. 1992  */
/* by Phil Lowder in Sumter, SC.            */
/* Compiled with MS QuickC.                 */

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

static void determine_video( void );
void do_lens(void);
void enter_diopter(void);
void check_bounds(void);
void set_kf(void);
void get_choice(void);
void do_again(void);

static void determine_video( void );
static unsigned int video_seg = 0;
static char _far *videoptr;
static int columns;

char text[80];
int color;
float kf;
float diopter1, diopter2;
float ideal, choice;

main()
{
   determine_video();
  _settextwindow(1, 1, 3, 80);
    if (color == 1)
      {
       _setbkcolor(5L);
       _settextcolor(14);
      }
   _clearscreen(_GWINDOW);

   _settextposition( 2, 30);
   _outtext("CONTACT LENS PROGRAM");

   enter_diopter();
   check_bounds();
   set_kf();
   get_choice();
   do_lens();
   do_again();
}

/*........................*/

void enter_diopter(void)
{
    if (color == 1)
      {
       _setbkcolor(1L);
       _settextcolor(7);
      }
    _settextwindow( 4, 1, 25, 80);
    _clearscreen(_GWINDOW);

    _settextposition(2, 20);
    _outtext("Enter First Diopter    ");
     scanf("%f", &diopter1);
     fflush(stdin);

    _settextposition(4, 20);

    _outtext("Enter Second Diopter   ");
     scanf("%f", &diopter2);
     fflush(stdin);
}

/*.......................*/

void check_bounds(void)
{
 int k;

   if ( diopter1 < 38 || diopter1 > 48)
      {
        _settextposition(3, 20 );
         _outtext("Diopter out of bounds ");
         do_again();
      }
        _settextposition(5, 20 );
   if ( diopter2 < 38 || diopter2 > 48)
      {
         _outtext("Diopter out of bounds ");
         do_again();
       }

}

/*................................*/

void set_kf(void)
{

 /* set kf to lesser diopter */

    if ( diopter1 <= diopter2)
      kf = diopter1;
    else
      kf = diopter2;

    if ( kf >= 38 && kf <= 40)
        ideal = 9.0;
    else if ( kf > 40 && kf <= 42)
        ideal = 8.5;
    else if ( kf > 42 && kf <= 44)
        ideal = 8.0;
    else if ( kf > 44 && kf <= 48)
        ideal = 7.5;

    _settextposition(7, 20);

   sprintf(text, "Ideal Diameter is      %.1f", ideal);
   _outtext(text);


}

/*................................*/

void get_choice(void)
{
 char kar;

    _settextposition(9, 20);
    _outtext("Lens Choices are");

   _settextposition(11, 25);
   _outtext("A.  8.9 ");
   _settextposition(12, 14);
   _outtext("Default ->");
    _settextposition(12, 25);
   _outtext("B.  9.3  ");
    _settextposition(13, 25);
   _outtext("C.  9.7  ");
    _settextposition(15, 20);
   _outtext("Enter lens choice      ");
  fflush(stdin);
  kar = getche();

   switch(kar)
    {
        case 'A':
        case 'a':
             choice = 8.9;
             break;
        case 'B':
        case 'b':
             choice = 9.3;
             break;
        case 'C':
        case 'c':

              choice = 9.7;
              break;
        default :
              choice = 9.3;
              break;
     }
}

/*...............................*/

void do_lens(void)
{
float correction, lens;
float x, y, z, i;

   /* find difference, a positive value */

        x = diopter1 - diopter2;
            if  ( x < 0 )
              x = diopter2 - diopter1;


  i = choice - ideal;

  correction = i * .12;

    if ( x < 1 &&  x > .75)
          x = .75;
    else if ( x < .75  &&  x > .5)
          x = .5;
    else if ( x < .5  &&  x > .25)
          x = .25;
    else if ( x < .25  &&  x > .0)
           x = 0;

  if ( x >= 1)
     y = kf + (x/4);
    else if ( x = .75)
       y = kf;
    else if ( x = .5)
      y = ( kf - .25 );
    else if ( x = .25 )
       y = kf - .37;
    else if ( x = 0 )
       y = kf - .5;


z = ( ( 1 / ( y /.3375)) * 1000 );

lens = z + correction;

   if (color == 1)
     {
      _setbkcolor(1L);
      _settextcolor(14);
     }
  _settextposition(17, 20);
    sprintf(text, "Lens =         %f", lens);
    _outtext(text);
}

/*................................*/

void do_again(void)
{
char ch;

     if (color == 1)
       {
        _setbkcolor(1L);
        _settextcolor(7);
       }

       _settextposition(19, 20);
    _outtext("Do another one? - (y)es");
     fflush(stdin);
     ch  =  getch();
        switch (ch)
         {
            case 'Y':
            case 'y':
                    main();
                    break;
            default :
                    exit();
                    break;
          }
}

/*.............................*/

static void determine_video( void )
{
    if ( !video_seg )
        {
           switch ( *((char _far *)0x449) )
             {
                 case 0:
                 case 1:
                 case 2:
                 case 3:
                     video_seg = 0xB800;
                     videoptr = (char far *)0xB8000000;
                     color = 1;
                     break;
                 case 7:
                     video_seg = 0xB000;
                     videoptr = ( char far *)0xB0000000;
                     break;
                 default:
                 printf( "not in text mode\n" );
                 exit(0);
             }
         columns = *( (int _far *)0x44A );
     }
}