need help with sin(x) and bar graph

Instructions:

You may use the template to organize your program.

No input from user is required.

x & y are float.

The function sin(x) is in the math.h header file and requires radians as input.

Must use a for loop.

Output MUST print to a file. However, you may also print to the screen.

Print a horizontal y axis using “-“. (Outside loop)

Print a vertical x axis using “|”. (Inside loop)

After finding the y value, print a scaled number of stars to represent y (inside loop).
Refer to bar graph code on p. 108.

Avoid mixed mode expressions.

Follow order of operations and precedence of operators.

i cant seem to figure out how to print all the stars in the sin(x) "shape" on x/y line when it prints to a file....i just need the top portion of the sin(x), help!

Code:

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

main()
{
  const float pi=3.1459;
  float x=pi,                  /*values for x in radians*/
        y=.0437;                    /*outputted number of stars*/


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

  FILE*joser=NULL;


  if((joser=fopen("c:outputfilename.txt","w")) ==NULL)
        printf("Error opening data file./n");
  else
  {
      for(i=0.0; i<=50.0;++i)

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

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

          fprintf(joser,"|\n");

        }
      y=sin(x);
      stars=(y*50+.5);
      for(y=0.0; x<=stars;++x)

      fprintf(joser,"*");

  }
  fprintf(joser,"|\nx");

  fclose(joser);




      system("PAUSE");
      return 0;
}

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Code:

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const float pi=3.1459;

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Why not

Code:

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double pi = atan(1) * 4;

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or 3.14159265358979... :)

Code:

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

---

No doubt you meant \n, not /n.

Code:

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

---

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

Code:

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

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Code:

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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:

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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:

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        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:

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

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Code:

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        stars=sin(x*pi/20)*60;

        for(y=stars;y<=60;++y)                  /*for loop to print the stars*/
            fprintf(fptr,"*");
        fprintf(fptr,"\n");        /*go to new line after printing a row*/

---

this is all that i changed, i forgot that i created "stars" so i took out g and replaced it with stars....

well, you gave me a pretty good idea on it, once i modified that graph, and ran the program, i got pretty damn close to what the txt file was supposed to look like now when i run it, i get

Code:

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____________________________________________________________ Y
|*************************************************************
|****************************************************
|*******************************************
|**********************************
|**************************
|*******************
|*************
|********
|****
|**
|**
|**
|****
|********
|*************
|*******************
|**************************
|**********************************
|*******************************************
|****************************************************
|*************************************************************
|
|
X

---

the curving is quite good, EXCEPT its supposed to be in a mountain shape, not caved in...lolz, but other than that, the coding is almost there....now i have to figure out how to reverse the arrangement of the stars to get my


**
***
*****
******
*******
******
*****
***
**


any thoughts?

Code:

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

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->

Code:

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

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perhaps?

Quote:

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Originally Posted by dwks

Code:

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

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->

Code:

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

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perhaps?

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thank you dwks, your help was quite enlightening, taking my programming "c" class, once a day per week for three hours doesnt quite make it into getting what i need to learn, even though i do come up with most of the code, you helped me finish it, thank you again...