i have some trouble with normals.

i have an application drawing lot of quads, for each quads i needs its normal.

so for each quad i have a loop that sounds like this :

glBegin(GL_QUADS);

glNormal3f(n0,n1,n2);

glVertex3f(i,random,j);

glVertex3f(i+1,random,j);

glVertex3f(i+1,random,j+1);

glVertex3f(i,random,j+1);

glEnd();

it is not exactly like this but it is the meaning .

the problem is that the values of normal is always 0.

what is wrong ?

talking of math i know that a normal for a surface is :

(v0-v1) x (v1-v2)

where v0,v1,v2 are 3 vertices of the surfaces.

in my case they are 3 vertices of my quad.