Need help Vertices program

This is a discussion on Need help Vertices program within the C Programming forums, part of the General Programming Boards category; I need help with my C program that reads the coordinates of the vertices of a polygon from a file? ...

  1. #1
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    Thumbs down Need help Vertices program

    I need help with my C program that reads the coordinates of the vertices of a polygon from a file?
    and computes the perimeter of the polygon.

    i got the basic program down i just get a weird error message about my distance formula function dist.

    heres my program:

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

    int main(void)
    {

    typedef struct {double x, y; } vertex_t;
    vertex_t temps;
    FILE *file;
    char flnm [64];
    double perim;
    vertex_t vertexs[20];
    double x; double y;


    printf("Enter the file name: "); /*gets file name*/
    scanf("%s",flnm);

    file = fopen(flnm, "r");

    double temps3;
    int input_status = fscanf(file,"%lf",&temps3);

    perim = 0;
    int i = 0;
    while(input_status != EOF)
    {
    input_status = fscanf(file, "%lf %lf",&x,&y);/*puts the points in the array*/
    temps.x = x;
    temps.y = y;
    vertexs[i] = temps;
    i++;
    }

    for(i=0;i<19;i++)
    {
    perim += dist(vertexs[i], vertexs[i+1]);
    }

    perim += dist(vertexs[0], vertexs[19]);

    printf("The perimeter is %f",perim);

    fclose(file);
    return 1;
    }

    double dist (vertex_t a, vertex_t b)/*gets the distance between two vertices*/
    {

    double distan;

    distan = sqrt(((b.x - a.x)^2) + ((b.y - a.y)^2));
    return distan;

    }


    the error messages i get are:

    [leahyp@pc20 hw8]$ gcc -Wall polygon.c
    polygon.c: In function 'main':
    polygon.c:39: warning: implicit declaration of function 'dist'
    polygon.c: At top level:
    polygon.c:50: error: expected ')' before 'a'


    please help me find whats wrong. i'm pretty sure its my distance function dist but idk what to do to fix it.

  2. #2
    Gawking at stupidity
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    The scope of your vertex_t struct (typedef struct {double x, y; } vertex_t is local to the main() function. Move it to just above (outside) your main() function and it should fix your problem.
    If you understand what you're doing, you're not learning anything.

  3. #3
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    omg haha thanks alot that makes complete sense. appreciate it alot!

  4. #4
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    Unhappy

    i moved it outside... but it's still not working :/

    Code:
    #include <stdio.h>
    #include <math.h>
    #include <unistd.h>
    #include <stdlib.h>
    
    typedef struct {double x,y;} vertext_t;    <-------
    
    
    int main(void)
    {
    
      vertext_t vertexes[20];
    and now i get a BUNCH of errors and warnings

    Code:
    polygon.c: In function 'main':
    polygon.c:41: warning: implicit declaration of function 'dist'
    polygon.c: At top level:
    polygon.c:52: error: conflicting types for 'dist'
    polygon.c:41: note: previous implicit declaration of 'dist' was here
    polygon.c: In function 'dist':
    polygon.c:57: error: invalid operands to binary ^ (have 'double' and 'int')
    polygon.c:57: error: invalid operands to binary ^ (have 'double' and 'int')

  5. #5
    spurious conceit MK27's Avatar
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    ^ is not for exponents in C, it's for XOR'ing. You need to use pow() from math.h.

    You need to declare a prototype for dist() at the top.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  6. #6
    DESTINY BEN10's Avatar
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    1. You should declare the prototype of dist() after the headers.
    Code:
    double dist (vertex_t a, vertex_t b); //note the semicolon
    2. pow() is the function that computes the power in C, not ^(which is XOR). So, in your dist function, use pow() instead of ^.
    Code:
    pow(x,y) //means x raised to the power y
    HOPE YOU UNDERSTAND.......

    By associating with wise people you will become wise yourself
    It's fine to celebrate success but it is more important to heed the lessons of failure
    We've got to put a lot of money into changing behavior


    PC specifications- 512MB RAM, Windows XP sp3, 2.79 GHz pentium D.
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  7. #7
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    alright i fixed the exponent problem and declared a prototype but i keep getting this weird error:

    Code:
    polygon.c:6: error: expected ')' before 'a'
    polygon.c: In function 'main':
    polygon.c:43: warning: implicit declaration of function 'dist'
    polygon.c: At top level:
    polygon.c:54: error: conflicting types for 'dist'
    polygon.c:43: note: previous implicit declaration of 'dist' was here

  8. #8
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    nevermind got it i just had to switch the order. nevermind

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