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Simple cycle

Started by kelvindavies11 May 31, 2006 at 6:40 AM 7 replies 900+ views

Original Post

May 31, 2006 at 6:40 AM

IM using the fllowing code to create a simple circle, which i intend to turn into a sphere. I knwo i could useing gluSphere however i fancy trying to do it this way. When i use the following code it gives me a syntax error on the '=', any idea why?? thanks, kelvin void cyclinder(void) { glBegin(GL_LINE_LOOP); for(int i=0;i<360;i++) { float xcoord = 1 * cos(i*2*PI/360); float ycoord = 1 * sin(i*2*PI/360); glVertex2f(xcoord,ycoord); } glEnd(); }

kelvindavies11

May 31, 2006 at 6:54 AM

i have amended the above code so it is simpler however im still getting the syntax error on the = sign. Any ideas?

void cyclinder(void)
{

glBegin(GL_LINE_LOOP);
for(int i=0;i<360;i++)
{
angle =2*PI*i/360;
glVertex3f(cos(angle),sin(angle), 1);
}

glEnd();

}

kind regards,
kelvin

AndyEsser

May 31, 2006 at 7:00 AM

I don't know much about C/C++ but isn't it supposed to be i==0?

Kalidor

May 31, 2006 at 8:52 AM

Which '=' is the error on? What is the exact error? Is PI defined? Is angle declared?

delta user

May 31, 2006 at 9:37 AM

First of all it is a bad idea to define "float xcoord" and "float ycoord" in your for loop because the OS needs to alloc memory for those variables everytime again. This causes a strain on performance. Declare them before your for loop or make them static.

I am using vc++ and it gives no errors.

But try typecasting.

xcoord = (float) 1 * cos(i*2*PI/360);

hope it works.
^_^

bakery2k1

May 31, 2006 at 9:49 AM

Quote:
Original post by AndyEsser
I don't know much about C/C++ but isn't it supposed to be i==0?

No, "i = 0" is correct.

Quote:

First of all it is a bad idea to define "float xcoord" and "float ycoord" in your for loop because the OS needs to alloc memory for those variables everytime again. This causes a strain on performance.

Any modern compiler will move the space "allocation" outside the loop for you. But, more importantly, since the code does not even compile for the OP, this is hardly is biggest concern right now.

kelvindavies11

May 31, 2006 at 12:18 PM

the aove does compile now, however when im using the above code i draw a circle however it only draws a circle containing 8 sides not the 360 that i require for a smooth circular effect.

any ideas please,
kelvin

bin11001010

May 31, 2006 at 12:46 PM

What is happening is i/360 is interger division. Change the line

angle =2*PI*i/360;

to

angle =2.0*PI*(float)i/360.0;

Also make sure that the variable angle is a float.

I do not have a CPP compiler in front of me but the floating point division instead of integer division will at least push you in the right direction.

kelvindavies11

May 31, 2006 at 1:58 PM

thanks i changed it to float but still no joy

kelvin

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