Top Down Approach and Bottom Up Approach

    

     Top Down Approach :                  

• It is also known as Step-wise design or Algorithmic decomposition or Divide and Rule.            
• Procedural programming Language follows top down approach. As C program is a Procedural Programming Language it follows top down approach/ Functional approach.
• It starts with high level system or design then it goes to low level system or design or development.
• In top down approach, first we are designing the main module(i.e main function) and in that we will decide what all other modules to be include then we will design all other sub modules.
• Top-down approach expects good planning and good understanding of the system or project.
•  Top-down approach means in C we first go in for declaring variable and function, then get into implementing them.

      

     Bottom Up Approach :

• Object Oriented Programming follows Bottom up approach.
• As C++ and Java are Object Oriented Programming Language it follows Bottom-up approach. 
•  Bottom up approach starts with low level system or design or development. Then it looks for high level system or design.
• Design all the sub modules related to application then we design main module and in that we will decide what are the modules to be include for ex: we can design any no of classes and in main only required classes and their functions can be used .
• Bottom-up approach means in C++ we first create the class(blue print) refers to how the objects look like and create objects for those classes then use them in our program.