Thread: beziers and arrays

Code:

         x[0]= x0; /*where is x0 defined*/
         y[0]= y0; /*where is y0 defined*/
         
         
         c=1;        /*are you implicitly defining c?*/
         u=1/100;/*here too*/
         gap=u;   /*this also???/*

         do
         {
                b0=pow((1-u),3);
                b1=3*pow((1-u),2)*u;
                b2=3*(1-u)*pow(u,2);
                b3=pow(u,3);

it crashes because you are writing memory you do not own(unless all those are global variables) You should really add -Wall -pedatic if on gcc and increase setting if your on something different like an IDE.
P.S. If you have all those defined pow returns double. the variable u must be at least a float and it would be 1.0/100.0

well, just to make sure theres no confusion as to exactly what i've done ill post the whole code. i noticed one little mistake (c+1 in the do loop was changed to c=c+1) and now i get a very nice error message.

The instruction at address 004011e9 attempted to write to location 00403000

the full code:

Code:

#pragma windows 500000,500000
#include <stdio.h>
#include <math.h>
#include<dbos\graphics.h>   
#include<windows.h>

float gap, u;
int w0, w1, w2, w3, b0, b1, b2, b3, x0, x1, x2, x3, y0, y1, y2, y3, c;

int a=300,b=300;
int x[100], y[100];

int draw()
        {
         x[0]= x0;
         y[0]= y0;
         
         
         c=1;
         u=1/100;
         gap=u;
         do
         {
                b0=pow((1-u),3);
                b1=3*pow((1-u),2)*u;
                b2=3*(1-u)*pow(u,2);
                b3=pow(u,3);
         
        
                x[c]=((b0*w0*x0)+(b1*w1*x1)+(b2*w2*x2)+(b3*w3*x3))/((b0*w0)+(b1*w1)+(b2*w2)+(b3*w3));
         
                y[c]=((b0*w0*y0)+(b1*w1*y1)+(b2*w2*y2)+(b3*w3*y3))/((b0*w0)+(b1*w1)+(b2*w2)+(b3*w3));
                
                c=c+1;
                u=u+gap;
         }
         while (u<=1);        
                  
        draw_bezier (x,y,100,RED);   
        return 1;
        }

int main()
{

int hand;

winio("%gr[grey]&", a, b);
winio("%lw&",&hand);
winio("x0: %rd\t&",&x0);
winio("x1: %rd\t&",&x1);
winio("x2: %rd\t&",&x2);
winio("x3: %rd\n&",&x3);
winio("y0: %rd\t&",&y0);
winio("y1: %rd\t&",&y1);
winio("y2: %rd\t&",&y2);
winio("y3: %rd\n&",&y3);
winio("w0: %rd\t&",&w0);
winio("w1: %rd\t&",&w1);
winio("w2: %rd\t&",&w2);
winio("w3: %rd\n&",&w3);
winio("%bc[red]%`^bt[Draw]\t",draw); 

}

One thing you should do and this is probably causing the error. Check your index variable 'c' prior to storing to the x and y arrays and make sure it's between 0 and 99. Like so:

if( c >=0 && c <= 99 ) /* store to x and y */
{
x[c] = /*your formula*/;
y[c] = /*your formula*/;
}

hmm, it has got rid of the error message, but now its just freezing out like before.

ok, after a good few hours of debuging i think i have found the source of the problem...but i cant see WHY it is a problem.

it seems as though the entire thing is woking (with some fudging to remove some bizare variable value swapping that was going on ) except this line:

Code:

u=(1/100);

it should obviously produce a value of 0.01 for u, however it is actually producing 0.0000. u is definied as a float, so i thought it would be ok. have i done something very silly, or is there another way of getting 0.01. it does not seem to like me simply putting the value into the code either. u=0.01; produces an error message.

Thanks Salem, changing 1 to 1.0 did the trick. Now its just a case of weeding out the few perculiarities and i'll be done.

Theres no reason why im using floats other than i didnt realise that i should be using double. why is a double superior in this situation?

ahh, ok then. thanks