Diffusion 2D solver for a steady system

First time writing a 2D diffusion solver using Finite Volume Method. I referred to Versteeg and Malalasekara for reference. This is a steady state solver. The boundary conditions at the ends are Dirichlet ones. With a little change in the solver, this can be changed into Neumann. Have fun tuning this to your needs.

The top plate temp = 400 K and the rest is at room temp = 298 K.