PGCHART: How to Draw a Line Chart with Lines Only

ID: Q68745

The information in this article applies to:

The C Run-Time (CRT), included with:
- Microsoft C for MS-DOS, versions 6.0, 6.0a, and 6.0ax
- Microsoft C/C++ for MS-DOS, version 7.0
- Microsoft Visual C++ for Windows, 16-bit edition, version 1.0

SUMMARY

In Microsoft C versions 6.0, 6.0a, 6.0ax, C/C++ 7.0 and Visual C/C++ 1.0 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.

MORE INFORMATION

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 6.0.


/* 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 2.5). 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( &amp;env, _PG_LINECHART, _PG_POINTANDLINE);

Get the array of current palette structures with the line: _pg_getpalette( palette_struct );

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 = ' '; 
```

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."

Additional query words: kbinf 6.00 6.00a 6.00ax 7.00 1.00


Keywords          : kb16bitonly 
Version           : 
Platform          : 
Issue type        :

Last Reviewed: July 26, 1999