Pseudocode, Finished; Implementation, Testing, and Maintenance

Tom Kelliher, CS17

Feb. 14, 1996

Pseudocode

See ``Pseudocoding Conventions,'' pp. 46--47

Top-Down Stepwise Refinement

The process of decomposing (``refining'') a problem (the ``top'') into sub-problems (``down'' a level), each of which may themselves be treated as problems and, therefore, further decomposed (``stepwise'').

Examples:

• Planning a vacation
• Determining the factors of a given positive integer
• Finding the ith largest number in a group of n numbers

Factor Finding

Initial pseudocode:

read and verify number
find and print number's factors
print a message if number is prime

read and verify number:

let number = 0
while number < 1
   begin
      print "Enter a positive integer: "
      read number
   end
end_while

find and print number's factors:

let prime = TRUE
let currentFactor = 2
let lastFactor = the square root of number truncated
   to an integer value
while currentFactor <= lastFactor
   begin
      if number is evenly divisible by currentFactor
         begin
            print currentFactor
            let number = number / currentFactor
         end
      else
         let currentFactor = currentFactor + 1
      end_if
   end
end_while

print a message if number is prime:

if prime == TRUE
   print "Your number is prime"
end_if

The ith Largest Number

Initial pseudocode:

determine n
determine i
read the n numbers into a list
arrange the n numbers in the list in descending order
pick out the ith number in the list and print it

Work on further refinement in small groups

We won't cover structure charts

Do we need to look at flowcharts?

Implementation

A computer program:

a sequence of a finite number of statements expressed in a programming language in a specific logical order which, when executed, produces the solution for a problem.

Compare algorithm

Programming Errors

• Design errors --- occur during analysis, design, implementation
• Syntax errors --- caught during compilation
  • warning messages
  • error messages
• Run-Time errors

Testing and Verification

• Program verification --- ensure program meets user requirements
• Program testing --- demonstrate program correctness

Are these the same?

What types of errors will each uncover?

How would you adequately test

• a program which computes averages?
• a program which finds the ith largest integer in n integers?
• the software which controls the Space Shuttle?

Documentation

Seemingly trivial, but important