Q68745: PGCHART: How to Draw a Line Chart with Lines Only

Article: Q68745
Product(s): See article
Version(s): 6.00 6.00a
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickc | mspl13_c
Last Modified: 29-JAN-1991

Using _pg_defaultchart, you can specify a line-chart type with
_PG_LINECHART. The choices for the chart style are _PG_POINTANDLINE
and _PG_POINTONLY. There is no manifest constant for "lines only," but
a line chart with lines only can be made with a few modifications to
the existing code, which produces a chart with points and lines.

The following code, which defines the field in the palette to be
modified, is taken from page 259 of the "Microsoft C Advanced
Programming Techniques" manual that shipped with C version 6.00.

/* Typedef for pattern bitmap */
typedef unsigned char fillmap[8];

/* Typedef for palette entry definition */
typedef struct
{
     unsigned short color;
     unsigned short style;
     fillmap fill;
     char plotchar;     /* by default, the plotted character is '*' */
}paletteentry;

/* Typedef for palette definition */
typedef paletteentry palettetype[ _PG_PALETTELEN ];

The following are the modifications to be made to the sample program
SCATTER.C, on pages 256-258 of "Microsoft C Advanced Programming
Techniques" (also on pages 280-281 of "C For Yourself," which was
shipped with QuickC version 2.50). Note that the original program
produces a scatter chart; a line chart requires different arguments in
the call to _pg_defaultchart(), as shown below.

Declare the following variable

   palettetype palette_struct;

after the line

   _pg_initchart( );

but before the line

   _pg_defaultchart( &env, _PG_LINECHART, _PG_POINTANDLINE);

1. Get the array of current palette structures with the line:

      _pg_getpalette( palette_struct );

2. Change the plotted character in the first palette to a blank, so
   that no points will appear on the graph (the line will be
   unbroken). For example:

      palette_struct[1].plotchar = ' ';

3. Reset the palette with the line:

      _pg_setpalette( palette_struct );

The following is the modified SCATTER.C program:

Sample Code
-----------

#include <conio.h>
#include <string.h>
#include <graph.h>
#include <pgchart.h>

#define MONTHS  12

typedef enum {FALSE, TRUE}  boolean;

float far value[MONTHS] =
{
        33.0,27.0,42.0,64.0,106.0,157.0,
       182.0,217.0,128.0,62.0,43.0,36.0
};

char far *category[MONTHS] =
{
        "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jly", "Aug",
        "Sep", "Oct", "Nov", "Dec"
};

palettetype palette_struct;

main( )
{
        chartenv env;
        int mode = _VRES16COLOR;

        if( _setvideomode( _MAXRESMODE ) == 0 )
                exit( 0 );
        _pg_initchart();

        _pg_getpalette( palette_struct );
        palette_struct[1].plotchar = ' ';
        _pg_setpalette( palette_struct );

        _pg_defaultchart( &env, _PG_LINECHART, _PG_POINTANDLINE );

        strcpy( env.maintitle.title, "Good Neighbor Grocery" );
        env.maintitle.titlecolor = 6;
        env.maintitle.justify = _PG_RIGHT;
        strcpy( env.subtitle.title, "Orange Juice vs Hot Chocolate" );
        env.subtitle.titlecolor = 6;
        env.subtitle.justify = _PG_RIGHT;
        strcpy( env.xaxis.axistitle.title, "Months" );
        strcpy( env.yaxis.axistitle.title, "Quantity" );
        env.chartwindow.border = FALSE;
        env.xaxis.ticinterval = 4.0;

        if( _pg_chart( &env, category, value, MONTHS ) )
        {
                _setvideomode( _DEFAULTMODE );
                _outtext( "Error: can't draw chart" );
        }
        else
        {
                getch();
                _setvideomode( _DEFAULTMODE );
        }
        return( 0 );
}

For more information about line charts, see pages 252-273 of
"Microsoft C Advanced Programming Techniques", and pages 267-296 of "C
for Yourself."

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