Explain Bottom up Approach with Advantages and Disadvantages.
Bottom-up Approach 
Bottom-up
programming is the opposite of top down programming. In bottom up approach all
the subtask are first coded into program and then interacted into increasingly
larger modules of the design, in the bottom up approach available set of
modules are first identified. An attempt is made to combine the lower
modules/subprograms to form modules of a high level.
This
process of combining modules is continued until the program is constructed. In
this approach quite after it is found that the final program obtained by
combining the predetermined lowest level modules does not meet all the
requirement of the desired program.
In a language such
as “C++” or “java”, bottom up programming takes the form of constructing
abstract data types.
Advantages
- The most important modules are written and tested first.
- It is easier for users or customers to see the progress being made in the project.
- Testing and debugging are easier and more efficient.
- The implementation is normally smoother and shorter.
- Programmer moral and job static function are increased.
- It is easier to detect and correct time delay and cost average runs.
- It is easier to deal with time delays and cost overruns when they occur.
- Data processing resources are used more evenly and efficiently.
Disadvantages
The basic drawback
of the bottom up approach is the assumption that the lowest level modules can
be completely specified beforehand, which in reality is seldom possible.