1.2
Steps
in Program Planning and Development
Programming is a problem-solving
activity. A person with good problem solving skills will tend to be good
programmers. To develop this skill, programmers practice the following steps:
1. problem
analysis
2.
setting up an algorithm
3. coding
4. encoding
5.
running, testing, and debugging
6. documentation
3
Chapter
1
1.2.1
Problem
Analysis
If we are to use the computer as a
problem-solving tool then we must have a good analysis of the problem given.
Here are some suggested steps on how to go about analyzing a certain problem
for computer application:
1.
Review the problem carefully and
understand what you are asked to do.
2.
Determine what information is given
(input) and what result must be produced (output).
3.
Assign names to each input and output
item.
4.
Determine the manner of processing
that must be done on the input data to come up with the desired output (i.e.,
determine what formulas are needed to manipulate the given data).
Example.
Given the scores for the two
departmental quizzes, two machine projects, final exam, and teacher's
evaluation, write a program that will compute for the final grade based on the
following computation:
50% Average of 2 departmental quizzes
+
15% Average of 2 machine projects
+
30%
Final
exam
+
5%
Teacher's
evaluation
--------------------------------------------------------
Quiz No. 1
- Qz1
Final Grade - FG
Quiz No. 2
- Qz2
Mach. Proj. 1
- Mp1
Mach. Proj. 2
- Mp1
Final Exam
- FE
Teacher's Eval. - TE
Qz1+Qz2 Mp1+Mp2
FG = 50% x ------------ + 15% x
----------- + 30% x FE + 5% x TE
2
2
1.2.2
Setting Up an Algorithm
After the problem has been clearly
defined, a list or sequence of steps that will solve the given problem must be
formulated. This sequence of steps is called an algorithm.
An algorithm can be described in many
ways. A natural language such as Filipino, English, or Chinese can be used but
we must be very careful that the 4
Introduction
to Computer Programming
algorithm be organized in a logical
and clear manner. Graphical forms or notations such as flowcharts can be used,
an improvement of the former, but is more sophisticated. It is important to
note that in whatsoever manner an algorithm is written, it remains to be NOT
executable simply because it cannot be entirely understood by the computer.
To cite an example, let us use the
final grade problem. A possible algorithm written in English that will solve
the problem would be:
1.
Get Qz1 and Qz2 scores.
2.
Get Mp1 and Mp2 scores.
3.
Get FE score.
4.
Get TE score.
5. Calculate
Qz1+Qz2
Mp1+Mp2
FG = 50% x ------------ + 15% x
----------- + 30% x FE + 5% x TE
2 2
6.
Display the final grade FG.
An algorithm may also be viewed as a
recipe. The manner in which the series of steps in a recipe is written is
similar to creating an algorithm. But, it should be noted that an algorithm is
more than a recipe. An algorithm has to be exact. An example statement in a
recipe would be “add salt to taste”. In an algorithm, this is not acceptable
because the statement is subjective and not quantifiable. Everything should be
definite.
1.2.3
Coding
After having set up the algorithm,
the next step is to convert this into a list of instructions in a code or
language that the computer can understand and execute. This process is called coding.
5
Chapter
1
Example.
Algorithm
Program
main()
{
float fQ1, fQ2;
float fMP1, fMP2;
float fFE, fTE, fFG;
Get Qz1 and Qz2 scores.
scanf("%f",
&fQ1);
scanf("%f",
&fQ2);
Get Mp1 and Mp2 scores.
scanf("%f",
&fMP1);
scanf("%f",
&fMP2);
scanf("%f", &fFE);
Get FE score.
scanf("%f",
&fTE);
Get TE score.
fFG = 0.50 * ((fQ1 +
Calculate FG.
fQ2)/2) + 0.15 *
((fMP1 + fMP2)/2) +
0.3 * fFE + 0.05 *
fTE;
Display the final grade
printf("FG = %.2f",
FG.
fFG);
}
The list of instructions that will
implement the algorithm can be understood by the computer simply because "it
is written in the vocabulary of the programming language and conforms to the
grammatical rules of the language."[LEES90] This list of instructions
understood by the computer is now called a program.
In the example above, we converted
our algorithm for computing the final grade to a C program. The scanf statements ask for input from the
user while the printf statement
displays the output.
1.2.4
Encoding
The process of entering the program
through a computer terminal directly into computer memory is called encoding.
1.2.5
Running, Testing, and Debugging
The fifth step in program development
would be to execute or run the program. The program is executed or run on
different input data. Testing is the art of creating 6
Introduction
to Computer Programming
different sets of sample data upon
which the program will be run. The programmer must submit the program to as
many combinations of test data as possible to anticipate and correct any error
that might come out before releasing the program to users. The process of
executing a program with test input data and checking the output results
against the requirements is referred to as desk
checking [PRAT96].
Errors that come out during program
execution are termed as bugs.
Computer programmers use terms as bug-ridden and buggy to describe a program
which is poorly written thus containing a lot of errors. The art of correcting
these errors is called debugging.
These bugs or errors can be
classified
into two groups: 1. syntactical or
logical errors;
Did you know that...
and 2. compile or run-time errors.
The term bug dates back
Syntactical
errors
result from failure to
to an old story about a group of
follow the syntax of the language. Syntax refers
programmers who couldn't
to the grammatical rules of the
language
figure out what was wrong with
defining its legal constructs.
Examples of which
their programs, until they
are unrecognized instructions,
missing
opened up the computer and
punctuation marks and misspelled
names.
found a moth trapped inside
[REGE87]
Logical
errors
are hard to identify.
What is erroneous here are the
outputs seen
onscreen which did not conform to or
match the
expected results. Such errors arise
during the
formulation of algorithm or in the
coding of the program that implements the algorithm due to the wrong analysis
or perhaps wrong approach of the programmer as he tackles the problem given.
Compile-time
errors
halt the compilation of the program. Compilation
means translating the program codes into a form that the physical computing
machine can understand. Program codes are translated completely so long as
their syntax is correct.
Once a syntax error is encountered
during compilation, this is considered to be a compile-time error.
Errors that appear during program
execution are called run-time errors.
Once a program starts running, it means that the program is already free of
syntax errors and compilation has successfully finished. However, it may still
have logical errors that may cause the abnormal termination of the program. An
example would be dividing a certain number by zero. Another would be the
program executing in an endless loop wherein the only way to stop it is to
manually stop the execution of the program.
7
Chapter
1
1.2.6
Documentation
There are three basic types of
documentation. The most common type of documentation is the user’s manual.
Software usually comes with a user’s manual and it contains information on the
software and hardware requirements, installation procedures, and step-by-step
instructions on how to use the system. This type of documentation is used by
the user of the program.
In the process of making sure that
the program is error-free, running correctly and efficiently, documentation of
the program must be done. The purpose of which is to maintain the relevance and
validity of the program. For the next two types of documentation, the process
must be continuous. Programs in real-world applications will likely be used for
a number of years and will probably require some modification as time passes.
Especially in large programs developed for complex projects, there will usually
be obscure bugs that do not become apparent until after the program has been
placed in use.[LEES90] Such modifications made due to further discovering
errors while the program is in use must be documented well. Ten years after the
program has been written, someone may want to update it and the first thing
he'll do is to look at the documentation of the program to become aware of the
details of the program. Good documentation reduces program maintenance efforts
and major problem reconstruction. These are the objectives of creating the
technical manual and internal documentation.
The technical manual is a printed
copy of the information regarding how the program was designed and how it was
created. Issues involved in choosing the data type or data structure, as well
as the algorithm for the solution, are also included. On the other hand, the
internal documentation has the same information but these are stored within the
program themselves, through the use of comments.
8
