Introducing Algorithms Dedric D. Owens
PRG/211 – Algorithms and Logic for Computer Programming
October 28, 2013
John Rogers

Describe the Top-Down Approach to Algorithm Writing When developing a program, the top-down approach is more than not the preferred method. This is driven by what the program actually does; basically the function of the program. According to Penn State Lehigh Valley, “top-down design or stepwise refinement is an approach to designing an algorithm” and, there are four steps in this top-down design. These steps are as follows: You have to “understand the problem by thoroughly analyzing it.” Then, “formulate the algorithm by determining and writing the main tasks to be carried out as a sequence of general steps”. The third step is to “fill in more details by determining the sub-tasks, if any, for each main task. Lastly, “repeat step third step until you arrive at a precise algorithm expressed in terms of basic executable instructions.”
How is pseudo-code used to assist in writing an algorithm? Pseudo-code is defined as an outline of a program written in a form that can easily be converted into real programming statements. It is sometimes confused with an algorithm when developing a program. In reviewing Prelude to Programming: Concepts and Design, Fifth Edition, (para. 2.1, pg 72 an algorithm is “a step by step method for solving a problem or doing a task.” Pseudo-code uses short and easy to understand phrases in plain English language to describe the outline of a program. Being able to use pseudo-code for an algorithm will make writing the actual code that much easier.
Why is spaghetti code considered a problem? The use of the term spaghetti code leads to assumption that it is bad code. This is not necessarily the case. Spaghetti code is low-level code where everything is everywhere. What makes spaghetti code dangerous is that it, unlike other species of bad code, seems to be a common byproduct of software entropy. In a blog post by Timothy Boronczyk, he states that “The phrase "spaghetti code" is an all-too-common pejorative we programmers use to describe horrible code, whether it's difficult to understand, poorly organized, or just plain long-winded. And there-in lays the problem. What really constitutes spaghetti code is subjective; I've yet to hear a concrete definition or standard metric that measures it. Everyone has his or her own opinion as to what aspects would make them label it spaghetti.”
What are the three control structures that are the basis for writing a program?

The three control structures are the sequential (or sequence) structure, the decision (or selection) structure, and the loop (or repetition) structure. The following definitions of each structure are taken from Prelude to Programming: Concepts and Design (para 2.5, pg 99-). A “sequential structure consists of a series of consecutive statements, executed in the order in which they appear. A decision structure (also known as a selection structure) there is

a branch forward at some point, which causes a portion of the program to be skipped. A loop

structure (also known as a repetition structure) contains a branch back to a previous statement in

the program module, which results in a block of statements that can be executed many times.

References
Venit, S and Drake, E (2011). Prelude to Programming: Concepts and Design (5th ed.).
Cornut, C (2011). Timothy Boronczyk’s Blog: Spaghetti Code Considered Harmful. Retrieved from http://www.phpdeveloper.org/news/16367
Penn State Lehigh Valley. Algorithms. Retrieved from http://www2.lv.psu.edu/ojj/courses/cpp-lang/02algorithmsqa.html