Thread: Creating graphs with 2 dimensional arrays

Hey guys. I have a question about how 2 dimensional arrays work. I am making a program that will graph functions (I'm starting easy like using 2x). To accomplish this, I am using a 2 dimensional array. Well, here is my question....

Code:

 This is what the graph will look like with 3 plotted points (they will be 'o''s  for my graph but to identify them I put the as x,y, and z).
x                             |
                              |
                              |
                              |
                              |
                              |
y---------------------------------------------------
                              |
                              |
                              |
                              |
                              |
z                             |

What index positions in the array are the points at? Example, what index positions are x, y, and z at? I guess I am trying to figure out how to loop through all the points on the graph and decide which index positions get a space, -, |, or o.

Thank you all for your help!

The positions would depend on the values in your array and how you interpret them.

Give it your best shot, post your code... I'm sure you'll get lots of help.

This is my attempt at creating the initial graph without the plotted function on it. Ignore the X-SEMIRANGE stuff, that was a #define. It doesn't work, but maybe you can point out my mistakes. Thanks so much guys.

Code:

char makeGraph()
{
     int x;
     int y;
     char graph[(Y_SEMIRANGE * 20) + 1][(X_SEMIRANGE * 20) + 1];
     for(y = 0; y < (Y_SEMIRANGE * 20) + 1; y++)
     {
           for(x = 0; x < (X_SEMIRANGE * 20) + 1; x++)
           {
                 if(x == X_SEMIRANGE / 2)
                      graph[y][x] = '-';
                 if(y == Y_SEMIRANGE / 2)
                      graph[y][x] = '|';
                 else
                     graph[y][x] = ' ';
                 printf("%c", graph[y][x]);
           }
     }
}

Post up what it is you're trying to graph. Something more than the first post? No challenge in that graph. I have no clue what you're stumped on.

You can take a screen shot of your screen (ctrl+PrnScr), paste it into your image viewer, and save it as a file. Then attach the file (using the manage attachments button near the bottom of the edit screen of the forum).

Think of your screen as a bunch of x and y points. You want to print from top to bottom rows, and from left to row columns.

The screen is your canvas.

Originally Posted by Adak

Post up what it is you're trying to graph. Something more than the first post? No challenge in that graph. I have no clue what you're stumped on.

You can take a screen shot of your screen (ctrl+PrnScr), paste it into your image viewer, and save it as a file. Then attach the file (using the manage attachments button near the bottom of the edit screen of the forum).

Think of your screen as a bunch of x and y points. You want to print from top to bottom rows, and from left to row columns.

The screen is your canvas.

I just want to make something that looks like this for now. If I could make this, I'm sure I can plot some function on it.

Code:

                                           |
                                           |
                                           |
                                           |
        -----------------------------------|-----------------------------
                                           |
                                           |
                                           |
                                           | 
                                           |

I have some reservations, but anyway:

Code:

#include <stdio.h>
#define MIDX 40
#define XMAX 41
#define MIDY 11
#define YMAX 18

int main() {
  int x,y; 
  printf("\n\n\n");
  for(y=0;y<YMAX;y++) {
     if(y==MIDY) {
      printf("--------------------------------------------------------------------------------");
    }
    for(x=0;x<XMAX;x++) {
      if(x!=MIDX)
        putchar(' ');
      else
        putchar('|');
    }
    putchar('\n');
  }

  printf("\n\n\t\t\t     press enter when ready");

  (void) getchar(); 
  return 0;
}

Am I going about this wrong?

This will initialize the graph array to all spaces, except the vertical and horizontal lines.

Code:

#include <stdio.h>

#define MIDX 38
#define XMAX 78
#define MIDY 11
#define YMAX 22

int main() {
  int i, j, r, c; 
  char graf[XMAX][YMAX];
  printf("\n\n ");
  for(i=0;i<YMAX;i++) {
    for(j=0;j<XMAX;j++) {
      graf[i][j]= ' ';
      if(i==MIDY)
        graf[i][j]= '-';
      if(j==MIDX)
        graf[i][j]= '|';
      putchar(graf[i][j]);
    }
    printf("\n ");
  }
  printf("\n\t\t\t     press enter when ready");

  (void) getchar(); 
  return 0;
}

On my screen, it's centered.

Thanks for your help Adak! I now have the the x and y axis correctly plotted.

Now for the last little push, how do I go about plotting a simple function on the graph?

Here is my attempt at a function to plot f(x) = 2*x;

Code:

char plot()
{
     double y, x;
     int X_INDEX, Y_INDEX, X_INT, Y_INT;
     for(x = -(X_SEMIRANGE); x < X_AXIS; x++)
     {
         y = f(x);
         Y_INT = intCast(y);
         X_INT = intCast(x);
         
         //this is where I am stuck
        
}

Ok, so how to I translate these numbers to the correct index positions?

I don't know.

You have to first decide which way the graph will increase: the direction of that increase. Will it be up from the bottom, or to the right side (from the left), or down from the top, or to the left, from the right hand side.

Look at some graphs and decide what you want. There are ALL kinds of graphs, and you need to know EXACTLY what you want, or your program will flop (or take forever to complete the code, because you'll want to keep changing it).

That's the next thing - you read up on graphs types, and decide what you want, how big your range of data will need to be (that helps decide the number of gradients that you will show), etc.

For a console display, you want to use only 75 horizontal X 22 vertical data points, max.

Here you have a vertical x axis and can change 3 display-parameters:
Ideone.com | R6kJV

Thanks for responses again. I'm ALMOST there! Let me post my code, bold the part that is causing me my (hopefully) final problem, and knock it out!

Code:

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

#define X_SEMIRANGE 3
#define Y_SEMIRANGE 3

double f(double); //prototype of the mathematical function to be graphed
char plot(); //prototype for the function that will plot the graph of f
char makeGraph(); //prototype for the function that intializes the graph to spaces and the x/y coordinates
int intCast(double); //prototype for the function that type casts a double to int correctly

double f(double x)
{
     return (2*x);
}

char makeGraph()
{
     int x, y, i, j;
     double xx, yy;
     int Y_AXIS = (Y_SEMIRANGE * 20) + 1;
     int X_AXIS = (X_SEMIRANGE * 20) + 1;
     int MID_Y = Y_AXIS / 2;
     int MID_X = X_AXIS / 2;
     int Y_INT, X_INT, Y_POS, X_POS;
     char graph[Y_AXIS][X_AXIS];
     
     for(y = 0; y < Y_AXIS; y++)  //This nest loop should create the x and y axis
     {
           for(x = 0; x < X_AXIS; x++)
           {
                graph[y][x] = ' ';
                if(y == MID_Y)
                     graph[y][x] = '-';
                if(x == MID_X)
                     graph[y][x] = '|';
                //putchar(graph[y][x]);
           }
           printf("\n");
     }
     //end creating x and y axis
     
     for(xx = -(X_SEMIRANGE); xx < X_AXIS; xx++)  //This loop should insert o's for all points on the function
     {
          yy = f(xx);
          Y_INT = intCast(yy);
          X_INT = intCast(xx);
          Y_POS = MID_Y + Y_INT;
          X_POS = MID_X + X_INT;
          graph[Y_POS][X_POS] = 'o';
     }
     
     for(i = 0; i < Y_AXIS; i++)  //This should loop through index positions and output the graph
     {
           for(j = 0; j < X_AXIS; j++)
           {
                 putchar(graph[i][j]);
           }
     }
}

int intCast(double x)
{
     int i = x;
     
     if (x >= 0)
         i = (int)(x + 0.5);
     else /* x < 0 */
         i = (int)(x - 0.5);
         
     return i;
}

int main()
{
   makeGraph();
   system("PAUSE");
   return 0;
}

The bolded code causes the program to crash. I think I have the right idea on how I am loading the o's on the graph (which are the plotted points on the function line). Am I doing this correctly, and am I outputting the graph correctly? Obviously I am wrong somewhere, because the program is crashing.

Thanks for the guidance!

Look at my code - you left out the putchar('\n'), after the inner loop. (the graph will be at the end of the row).

You should be getting a warning or an error message from your debugger/compiler. I don't know what the heck you're doing with SEMIRANGE stuff.

Nobody knows your code better than you do, and you can step through it in your debugger, as well or better, than anyone else. You're the right person to debug that.