PGCHART: How to Draw a Line Chart with Lines Only

 Last reviewed: July 17, 1997
Article ID: Q68745
6.00 6.00a 6.00ax 7.00 | 1.00 
MS-DOS                 | WINDOWS
kbprg kbcode

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, 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( &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 reference words: kbinf 6.00 6.00a 6.00ax 7.00 1.00
    KBCategory: kbprg kbcode
    KBSubcategory: CRTIss
    Keywords : kb16bitonly

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    Last reviewed: July 17, 1997
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