OpenGL: Trying to create a solid cylinder using triangle_fan - opengl

Question

I am trying to create a solid cylinder using triangle fan.
What I've done so far is this:
float base = 0.5;
float height = 20;
float radius = 2.0f;
glBegin(GL_TRIANGLE_FAN);
for(float j=0; j<=height; j+=0.1)
{
glVertex3f(0,j,0);
for(int i=0; i<360; i++)
{
glVertex3f(radius*sin((float)i),j, radius*cos((float)i));
}
}
glEnd();
glPopMatrix();
The problem appears in these 3 screenshots:
As you see in all 3 screenshots there appears to be some space and not a solid cylinder.
Is that ok?

Answer 1

First thing you should pay attention to (Edit: I slightly misread your code. You are doing fine with the triangle fan) is that a triangle fan works like this:
glVertex: Center point
for each outer point p
glVertex: p
For example:
p2__
/| ---___p1
/ | /
/ | /
p3/ | /
|\ | /
| \ | /
| \_O Center
| __---
p4
Second thing is that a cylinder consists of three parts:
__
/ \
\__/ <---- circle on top (facing up)
| |
| |
| |
| | <---- tube in the middle
| |
| |
| |
\__/ <---- circle on the bottom (facing down)
So the algorithm you need is:
/* top triangle */
glBegin(GL_TRIANGLE_FAN);
glVertex3f(0, height, 0); /* center */
for (i = 0; i <= 2 * PI; i += resolution)
glVertex3f(radius * cos(i), height, radius * sin(i));
glEnd();
/* bottom triangle: note: for is in reverse order */
glBegin(GL_TRIANGLE_FAN);
glVertex3f(0, 0, 0); /* center */
for (i = 2 * PI; i >= 0; i -= resolution)
glVertex3f(radius * cos(i), 0, radius * sin(i));
/* close the loop back to 0 degrees */
glVertex3f(radius, height, 0);
glEnd();
/* middle tube */
glBegin(GL_QUAD_STRIP);
for (i = 0; i <= 2 * PI; i += resolution)
{
glVertex3f(radius * cos(i), 0, radius * sin(i));
glVertex3f(radius * cos(i), height, radius * sin(i));
}
/* close the loop back to zero degrees */
glVertex3f(radius, 0, 0);
glVertex3f(radius, height, 0);
glEnd();
The way you were trying to do is first, not correct, since you are not actually making a cylinder, but stacking many circles, and second is inefficient since you are filling in space that is mostly invisible (the inside of the cylinder).

Answer 2

for(int i=0; i<360; i++)
{
glVertex3f
(
radius*sin((float)i),
j,
radius*cos((float)i)
);
}
The C standard library sin() and cos() functions take radians, not degrees.
Try converting (float)i to radians before you pass it to sin()/cos().