Problem with loops

[yesimwearingpants]

I am trying to alternate colors so I used this loop
float j;
do {
if(j==.8){
//b for blue
b = uv.y+j;
j -= .1;
} else if ( j== .4){
b = uv.y+j;
j -= .1;
} j=.4;
} while (j!=1.0);

It freezes and crashes on compile. I wanted to use
ctime for a delay but is there a better way I
should be doing this, I an Very new too OpenGL

[markusfisch]

I'm sorry, I don't quite understand what you're trying to do. If you're simply trying to alternate colors, it's better to use math instead of conditional statements.

Something like:

gl_FragColor = vec4(
    sin( time*0.2 ),
    sin( time*0.3 ),
    sin( time*0.4 ),
    1.0 );

Please have a look at the GLSL documentation and check out a few simple shaders from here or here.