Problem(s) with my program ( involves using arrays)

[canteyn]

Ok here is my problem. I am coding a program that uses 3 different functions, and the end result is that the program reads in (x,y) points from a file, and then outputs those points to another file, and then calculates the area of the points(which form a polygon). I am able to compile the program just fine, but every time I try and run the program I just get a "segmentation fault". It may be in regards to my arrays, in fact I am almost sure that is what the problem is, however I could be completely wrong.

Here is what my input file looks like:
4 0
4 7.5
7 7.5
7 3
9 0
7 0
4 0

The end result in my output file should look like this:

x y
-----------
4 0
4 7.5
7 7.5
7 3
9 0
7 0
4 0
======
Area: 25.5 square units

And now finally here is the code

/* 
    File Name: lab6.c
    Author:  Nick Cantey
    Description:  This program computes the area of a polygon with at most 20
                  points (includes counting the starting point twice).
*/
 
#include <stdio.h>
#include <math.h>
 
int get_corners(FILE*, double*, double*);
void output_corners(FILE*, double*, double*, int);
double polygon_area(double*, double*, int);
 
int main()
{
double area;
int n; /* variable for the number of points */
double xArray[20]; /* variable for the array that holds the x values */
double yArray[20]; /* variable for teh array that holds the y values */
FILE* in; /* allows the program to open outside files */ 
FILE* out; /* allows the program to send information to outside files */
 
/* Opens and closes the input file and calls the get_corners function */
in = fopen("lab6.in", "r");
n = get_corners(in, xArray, yArray);
fclose(in);
 
/* Opens the output file and calls output_corners and polygon_area */
out = fopen("lab6.out", "w");
output_corners(out, xArray, yArray, n);
area = polygon_area( xArray, yArray, n);
printf("=========\n");
printf("Area:  %lf square units", area);
/* Closes the output file */
fclose(out);
 
 
}
 
 
/*
    Function Name:  get_corners
    Parameters:  in, xArray, yArray
    Description:  This function fills the arrays with the point information   
*/
 
int get_corners(FILE* in, double* xArray, double* yArray)
 
{
int number, i;
 
/* Starts the for loop and reads the points into their respected arrays */
while(fscanf(in, "%lf%lf", &xArray[i], &yArray[i]) !=EOF)
    {
      i++;  
    }
number = i;
 
return(number); 
}
 
/*
    Function Name:  output_corners
    Parameters:  out, xArray, yArray, n
    Description:  Outputs the x,y coordinates in a table to lab6.out file
*/
 
void output_corners(FILE *out, double *xArray, double *yArray, int n)
 
{
int i; 
 
printf("x     y\n---------\n");
 
for(i = 0; i <= n; i++)
     {
       printf("%lf      %lf\n", &xArray[i], &yArray[i]);
     }
}
 
/*
     Function Name:  polygon_area
     Parameters:  xArray, yArray, n
     Description:  Calculates the area of the polygon and returns it
*/
 
double polygon_area(double* xArray, double* yArray, int n)
 
{
double area;
int i;
 
for(i=0; i <= n; i++)
     {
       area = (yArray[i]*i+1-yArray[i])*(xArray[i]*i+1+xArray[i]);
     }
area = area*0.5;
return(area);
}
 

I have spent all day today trying to fix this program, and I think I have just gotten myself into a loop, and I am unable to recover. PLEASE HELP :D

[gpraghuram]

HI,
I tried your code in my cygwin and compiled using gcc.
It ran successfully.
I have made quiet a few changes.

/* 
    File Name: lab6.c
    Author:  Nick Cantey
    Description:  This program computes the area of a polygon with at most 20
                  points (includes counting the starting point twice).
*/
 
#include <stdio.h>
#include <math.h>
 
int get_corners(FILE*, double*, double*);
void output_corners(FILE*, double*, double*, int);
double polygon_area(double*, double*, int);
 
int main()
{
double area;
int n; /* variable for the number of points */
double xArray[20]; /* variable for the array that holds the x values */
double yArray[20]; /* variable for teh array that holds the y values */
FILE* in; /* allows the program to open outside files */ 
FILE* out; /* allows the program to send information to outside files */
 
/* Opens and closes the input file and calls the get_corners function */
in = fopen("lab6.in", "r");
n = get_corners(in, xArray, yArray);
fclose(in);
 
/* Opens the output file and calls output_corners and polygon_area */
out = fopen("lab6.out", "w");
output_corners(out, xArray, yArray, n);
area = polygon_area( xArray, yArray, n);
printf("=========\n");
printf("Area:  %lf square units\n", area);
/* Closes the output file */
fclose(out);
 
 
}
 
 
/*
    Function Name:  get_corners
    Parameters:  in, xArray, yArray
    Description:  This function fills the arrays with the point information   
*/
 
int get_corners(FILE* in, double* xArray, double* yArray)
 
{
int number, i;
 
/* Starts the for loop and reads the points into their respected arrays */
while(fscanf(in, "%lf%lf", &xArray[i], &yArray[i]) !=EOF)
    {
      i++;  
    }
number = i;
 
return(number); 
}
 
/*
    Function Name:  output_corners
    Parameters:  out, xArray, yArray, n
    Description:  Outputs the x,y coordinates in a table to lab6.out file
*/
 
void output_corners(FILE *out, double *xArray, double *yArray, int n)
 
{
int i; 
 
fprintf(out,"x     y\n---------\n");
 
     for(i = 0; i < n; i++)
     {
       fprintf(out,"%lf      %lf\n", xArray[i], yArray[i]);
     }
}
 
/*
     Function Name:  polygon_area
     Parameters:  xArray, yArray, n
     Description:  Calculates the area of the polygon and returns it
*/
 
double polygon_area(double* xArray, double* yArray, int n)
 
{
double area;
int i;
 
     for(i=0; i < n; i++)
     {
       area += (yArray[i]*i+1-yArray[i])*(xArray[i]*i+1+xArray[i]);
     }
area = area*0.5;
return(area);
}
 

Thanks
Raghuram

[canteyn]

thanks for looking into my problem, by chance do you think you could help me out and let me know what changes you made and where so I may be able to see my mistakes and make the proper corrections. thanks again!

[canteyn]

disregard that one post ......
however I did try your code that you repost with the corrections and it still is giving me a segmentation fault :/ .... any ideas why that may be.

[gpraghuram]

Hi,
I ran the code in cygwin using g++.
Which OS/compiler r u using?

Thanks
Raghuram