creating my first simple geometry shader - opengl

Question

I'm trying to create the simplest geometry shader ever.
I have a working vertex and fragment shaders and I'm drawing triangles with
glDrawElements(GL_TRIANGLES, size, GL_UNSIGNED_INT, 0);
Vertex Shader:
// vertex shader
#version 120
attribute vec3 in_position;
uniform mat4 modelViewProjectionMatrix;
void main() {
gl_Position = modelViewProjectionMatrix * vec4(in_position, 1.0);
}
Fragment Shader:
// fragment shader
#version 120
void main() {
gl_FragColor = vec4(1.0,0.0,0.0,1.0);
}
Geometry Shader
//geometry shader
#version 120
#extension GL_EXT_geometry_shader4: enable
void main(void) {
for (int i = 0; i < gl_VerticesIn; i++) {
gl_Position = gl_PositionIn[i];
EmitVertex();
}
EndPrimitive();
}
my compile method which compiles all my shaders works without returning any gl_error
This is my attach and link method and this is where I get when I try to specify the output values for my shader
void attached_and_link_shaders() {
glAttachShader(programid, shaderV);
glAttachShader(programid, shaderG);
glAttachShader(programid, shaderF);
glProgramParameteriEXT(programid, GL_GEOMETRY_INPUT_TYPE_EXT, GL_TRIANGLES);
gl_error("EXT INPUT TYPE");
// error here
glProgramParameteriEXT(programid, GL_GEOMETRY_OUTPUT_TYPE_EXT, GL_TRIANGLES);
gl_error("EXT OUTPUT TYPE"); // OUTPUT TYPE 1281 invalid value
glProgramParameteriEXT(programid, GL_GEOMETRY_VERTICES_OUT_EXT, 3);
gl_error("EXT VERTICES OUT");
glLinkProgram(programid);
}
Where could my problem be? any references to good geometry shader tutorials for version 120 would be helpful,
Edit my out vertices were in correct, the solution is using GL_TRIANGLE_STRIP
my problem is solved and I feel like crying
Thanks