How to reclassify a raster into discrete classes for suitability analysis?

Reclassifying a continuous raster into discrete class is a very common analysis in GIS mainly done for site suitability and other multicriteria decision analysis. In this tutorial, we will be using raster calculator of QGIS to reclassify a road data into various classes for a site suitability. The concept presented here can be used to reclassify any kind of raster like slope, road, settlement, river data etc.