Thread: need help with sin(x) and bar graph

Code:

const float pi=3.1459;

Why not

Code:

double pi = atan(1) * 4;

or 3.14159265358979...

Code:

printf("Error opening data file./n");

No doubt you meant \n, not /n.

Code:

        fprintf(joser,"_");
        fprintf(joser,"y\n");

Does that really warrant two calls to fprintf()? . . . and did you mean something like this?

Code:

fprintf(joser, "_%f\n", y);

Code:

for(x=0.0 ;x<=20.0;++x)

Using floating point numbers to control a loop is a bad idea for accuracy reasons, especially when you're not using the loop variable in the loop body itself.

well, im fiddling around with the code and i think im almost there, i just need to make it so that when it writes to a .txt file, it prints out an X and Y lines along with STARS that resemeble the SIN(x) graph, just the top portion, but all i get are just plain stars all the same lengths....this is what the program is supposed to do, print to a .txt file this:
_________y
|*
|**
|***
|****
|***
|**
|*
x


except supposed to be around as long as the Y graph....how do i calculate it into this code???This program should graph the funcion y=sin(x)
on the interval from 0 to pi in incriments of pi/20.

Code:

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

main()
{
   const float pi=3.1459;
   float x,                   /*values for x in radians*/
         y;                    /*outputted number of stars*/

   int stars,
       i =0.0;      /*number of stars graphed*/

   FILE*fptr=NULL;


   if((fptr =fopen("c:outputfilename.txt","w")) ==NULL)      /*test if files opened correctly*/
      printf("\nError opening file\n\n");
   else
   {
      for(i=1; i<=60; ++i)                                   /*for loop to print the y axis*/
         fprintf(fptr,"_");
      fprintf(fptr," Y\n");



      for(x=0; x<=20.0; ++x)                            /*for loop to calculate the function*/
      {                                                /*values and the number of stars*/
         int g;
         g=sin(x*pi+1);
         fprintf(fptr,"|");                                /*prints the x-axis*/


         for(y=g ;y<=20.0;++y)                   /*for loop to print the stars*/
            fprintf(fptr,"*");
         fprintf(fptr,"\n");         /*go to new line after printing a row*/
      }                              /*of stars*/
      fprintf(fptr,"|\n|\nX");

      fclose(fptr);
   }

   system("pause");
   return 0;
}

Code:

if((fptr =fopen("c:outputfilename.txt","w")) ==NULL)

I never understood the rationale behind using full path names with fopen(). Just use the current directory! It's shorter and it's more convenient for the user. It' more portable: maybe you only have write access to the current directory. Maybe there isn't a c: drive, or the main drive is d: or something. Maybe the user doesn't want a file called outputfilename.txt suddenly appearing on the root of their drive. Maybe the user is running Linux, in which case fopen() will balk at that strange-looking filename, or you'll get a file called 'c:outfilefilename.txt'.

Now that that rant's out of the way . . .

Code:

         int g;
         g=sin(x*pi+1);

Who gave you that algorithm? Because it's not right.

What you want is for the parameter to sin to vary from 0 to PI, so that you get that sine-curve you're looking for. Since x goes from 0 to 20, you need to divide x by 20, to get it to vary from 0 to 1, and then multiply that by PI, so that it varies from 0 to PI, which is what you want.

Okay. Now the return value of sin() will be from 0 to 1. Since you want a bar graph that is (presumably) 60 wide, you need to multiply the return value of sin by 60.

In other words:

Code:

g = sin(x * pi / 20.0) * 60.0;

Code:

for(y=stars;y<=60;++y)

->

Code:

for(y=0;y<=stars;++y)

perhaps?