C++ OpenGL flickering Issues - c++

Question

Im having a Problem, where when I just render 1 Cube it's all okay, but if I add multiple Cubes all of them start flickering.. might be because they are intefering each other but im using double dubbers so it shouldn't be that. here the code of the render method
for (std::vector<Entity *>::iterator iterator = entityArray->begin(); iterator != entityArray->end(); iterator++) {
Entity *entity = *iterator;
if (entity->getVertexBuffer() != NULL) {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(entity->getVertexBuffer()->getShader()->getProgramHandle());
glLoadIdentity();
gluLookAt(_currentCamera->getPosition().x,
_currentCamera->getPosition().y,
_currentCamera->getPosition().z,
_currentCamera->getEyeVector().x,
_currentCamera->getEyeVector().y,
_currentCamera->getEyeVector().z,
_currentCamera->getUpVector().x,
_currentCamera->getUpVector().y,
_currentCamera->getUpVector().z);
glTranslatef(entity->getPosition().x, entity->getPosition().y, entity->getPosition().z);
glRotatef(entity->getRotation().x, 0.0f, 0.0f, 1.0f);
glRotatef(entity->getRotation().y, 0.0f, 1.0f, 0.0f);
glRotatef(entity->getRotation().z, 1.0f, 0.0f, 0.0f);
glScalef(entity->getScale().x, entity->getScale().y, entity->getScale().z);
glUniform4f(entity->getVertexBuffer()->getShader()->get_uColor(),
entity->getVertexBuffer()->getShaderData()->get_uColorValue().x,
entity->getVertexBuffer()->getShaderData()->get_uColorValue().y,
entity->getVertexBuffer()->getShaderData()->get_uColorValue().z,
entity->getVertexBuffer()->getShaderData()->get_uColorValue().w);
glUniform3f(entity->getVertexBuffer()->getShader()->get_uLightPosition(),
entity->getVertexBuffer()->getShaderData()->get_uLightPosition().x,
entity->getVertexBuffer()->getShaderData()->get_uLightPosition().y,
entity->getVertexBuffer()->getShaderData()->get_uLightPosition().z);
entity->getVertexBuffer()->configureVertexAttributes();
entity->getVertexBuffer()->renderVertexBuffer();
glfwSwapBuffers(_window);
glfwPollEvents();
}
}

Answer 1

Clear first, draw all cubes, then swap, like this:
glClear();
for (cube in cubes) { draw(cube); }
glfwSwapBuffers(_window);
glfwPollEvents();
That should solve it.

Answer 2

You're calling glClear and glSwapBuffers in the inner loop. So for everything you draw in the inner loop, it clears the picture, draws the thing (a single cube) swaps and then does the same for the next element in the array.
Everything that does not draw a cube must go outside of that loop.