CS 211 Lesson 9

An Overview of Basic Programming

Quote:

Character isn't inherited.  One builds it daily by how one thinks and acts Helen Gahagan Douglas

Lesson Objectives:

• To review the first eight lessons

• To review the important aspects of program creation, basic mathematical operations, and program control structures

• To emphasize the concept of "readable" code

Lesson:

I. MATLAB Concepts

• This is a review lesson -- no new MATLAB concepts are introduced.
   

• If you have not learned the material in previous lessons, please take the time required to review the material in those lessons.

II. Good Programming Practices

A. Review of programs

• A MATLAB program consists of one (or more) functions in an m-file.

• The m-file name should have the same name as the function it contains.

• A good program requires:

  • "Readable" code that can be corrected and enhanced in the future by either the original program author or by different programmers.

  • Well documented code that facilitates future corrections and enhancements.

  • Efficient code that will execute in a reasonable amount of time.

• The major cost of real-world software is not its original development costs, but rather the cost of future corrections and enhancements.

B. Creating "readable" code

• "Readable" code is a series of MATLAB statements that facilitate quick understanding of the code's intent.

• Consider the two coding examples below, both of which perform the exact same task. Which is more "readable"?

  B = 1; C = input('Enter a number: '); D = C; while abs(B - D) > 0.00001 D = B; B = (D + C/D)/2; end fprintf('The answer is %f.\n', B)

  Error_tolerance = 0.00001; New_guess = 1; N = input('Enter a positive number: ');   Old_guess = N; while abs(New_guess - Old_guess) > Error_tolerance      Old_guess = New_guess;      New_guess = (Old_guess + N/Old_guess)/2; end   fprintf('The square root of %f is approximately %f.\n', ...         N, New_guess)

• "Readable" code typically has the following characteristics:

  • Good, descriptive variable names.

  • Code statements that are grouped into related blocks by separating them from other code blocks with a blank line.

  • Code statements that are indented inside branches and loops to indicate selection or repetition.

  • Very descriptive prompts in input statements.

  • Very descriptive and well formatted output statements.

  • The creation of "constants" for important values (e.g., Error_tolerance in the above code).

C. An example program

• Please use this sample solution from a previous semester's PEX 1 assignment as an example of good, well documented, readable code.

III. Algorithms

A. How to access "relative" values in an array

• It is very common to calculate the position (index) of an array element.

• For example, consider the problem of calculating a Fibonacci series, which is defined as follows:

  f₀ = 1
  f₁ = 1
  f_n = f_n-1 + f_n-2,  for all n >= 3
  
  The first 8 terms are: 1  1  2  3  5  8  13  21 ...

• One algorithm for calculating such a series uses an array to store previous values of the series and looks like the following:

  n = input('Enter the Fibonacci term to calculate: ');
  Values = ones(1,n);
  for j = 3:n
    Values(j) = Values(j-1) + Values(j-2);
  end
  fprintf('The %d term is %d\n', n, Values(n) );

• Notice the use of calculations to get the appropriate index values into the array.

Lab Work: Lab 9

References:  (none)