Accessing an array

use the following:
for (x = 0; x < 310; x+= 3)
{
angle = 2.0*(float)PI*x/100;
radius = 0.5f * (2+sin(8 * angle));
ar[x] = radius * cos(3*angle);
ar[x+1] = radius * sin(8*angle);
ar[x+2] = radius * sin(3*angle);
}

Each element must be put into the location of the array one at a time

[EDIT: bad answer deleted]

-me

I forgot to say you probibly also have to allocate memory from the heap for such a large array e.g.

int* pAr = new int[310];

then use the array
for (x = 0; x < 310; x+= 3)
{
angle = 2.0*(float)PI*x/100;
radius = 0.5f * (2+sin(8 * angle));
*(pAr+x) = radius * cos(3*angle);
*(pAr+x+1) = radius * sin(8*angle);
*(pAr+x+2) = radius * sin(3*angle);
}

then before the program terminates use
delete pAr

NOTE: x is incremented by 3 in the for loop not by 1 ->
not size*3!!!! This will allocate way more memory than needed

Quote:

Original post by CryonicGhost I forgot to say you probibly also have to allocate memory from the heap for such a large array e.g. int* pAr = new int[310]; then use the array for (x = 0; x < 310; x+= 3) { angle = 2.0*(float)PI*x/100; radius = 0.5f * (2+sin(8 * angle)); *(pAr+x) = radius * cos(3*angle); *(pAr+x+1) = radius * sin(8*angle); *(pAr+x+2) = radius * sin(3*angle); } then before the program terminates use delete pAr

even when you allocat from the heap you don't need to access your array with pointer arithmatic. you can use normal code:



-me

Quote:

Original post by CryonicGhost NOTE: x is incremented by 3 in the for loop not by 1 -> not size*3!!!! This will allocate way more memory than needed

yep. you're right. my bad :) it's getting late...

-me

Sweet dude - didnt know that about pointers so we even :)

Try something like this. It should draw a circle with radius 1 on the XY plane. I'm not quite sure how your values work in your example, so I'm going to start from scratch.

Anyway, here's my version:

// some variablesfloat ar[90][3]; // 90 points of x,y,zfloat angle, radius;int i;// calculate the arrayfor(int i=0; i<90; i++){   angle = i*PI/45;   radius = 1;   ar[0] = radius * sin(angle); // x   ar[1] = radius * cos(angle); // y   ar[2] = 0;                   // z}// draw the circle from values in the arrayglBegin(GL_LINE_LOOP);   for(i=0; i<90; i++) glVertex3fv(ar);glEnd();

Your code has two errors. The first one is this line:

ar[x] = radius * cos(3*angle), radius * sin(8*angle), radius * sin(3*angle);

Here, you assume that commas allow you to assign values to consecutive indices in the array. When used like this, commas are more like the equivalents of semicolons. So, ar[x] is getting the value radius*cos(3*angle), and the other two comma-seperated statements are just creating a float value which is then ignored.

Next is this line:

glVertex3fv(ar[x]);

glVertex3fv expects a pointer to a float, and you are passing it a float value. ar[x] returns the value stored at index x, not a pointer to it. To do that you'd have to pass either &ar[x] or ar+x.

I suggest you find a copy of The C Programming Language by Kernighan and Ritchie, and read it cover to cover. Normally I would suggest some online tutorial, but I have yet to see one which sufficiently covers some of the little details, especially the bit about how commas work.

Hope that helps.

[edit] 6 other replies in the time it took me to type that... a new record! [/edit]

Thanks for all the replies, I was able to get it to work using the [90][3] array. I got a cool flower shape out of it =P
Thanks again to everyone!