What is the difference between top-down and bottom-up, programming?

Ans: Top-down and Bottom-up Approaches

In Top-down programming approach, we begin by identifying the main modules of the program, decomposing them into their lower modules and iterating unless the desired level of detail is achieved. This is also termed as Step Wise Refinement; Beginning from an abstract design, in every step the design is refined to a more concrete level until we reach a level where no more refinement is required and the design can be executed directly, whereas in Bottom-up programming approach, modules that are needed by programs and decide how to join these modules to provide larger ones; to join those to give even larger ones, and so on, till we arrive at single big module which is the whole of the desired program. In Bottom-up approach, we require to use a lot of intuition to decide exactly what functionality a module should give. This is not the case in Top-down approach.