Roxy

I am a student majoring in Security. We are taking a programming class and I am not understanding the structure part at all. I know a structure is a basic unit of programming logic and each sturcture is one of the following: sequence, selection, and loop. What is an acceptable sturctured program though? The book gives all these illustrations with a big DON'T beside them, I am confused.

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jcjacob

Structured programming enforces logical structure to make the program more efficient, easy to understand and maintain.

Large routines are broken down into smaller modules, and use of the GOTO statement is strongly discouraged

Let's say you have a program that reads a data file line by line, processes the data and prints it.

A structured program may look like this:

Open File
While (end of file is not reached)
read line of data
if (error condition)
Call Error routine
end program
end if
Call routine to process and print data
end while
end program

The same program that does not use structured programming might look like this:

Open file
LABEL1:
read line of file
if there was data
process data....
print data....
else
GOTO LABEL2
GOTO LABEL1
LABEL2:
exit program

Even in this simple example, you can see that it can easily become hard to follow, and the chance of introducing bugs increases as the lines of code increase.

I hope this helps answer you question. If not, post again and we'll give it another shot.

__________________
-John

Roxy

Thanks John, That makes more sense than the book. Can you place a sequence within the true half of a dual alternative decision in a structured program? This is just one of the questions the book ask. I know that the dual alternative is used in the selection structure but can it be used in the sequence structure, since sequence you follow an action in a task in order? I really like the programming part that I have learned so far but not sure about structures.

jcjacob

Yes, you certainly can.

In a single alternative structure, if a condition is true, you do something, if it's false, you do nothing. In a dual-alternative basically means that if a condition is true, you do something, and if it's false, you do something else.

Within that IF construct, IF something is true, you might do some things. If it's false, you might do other things.

For example:

If today = Monday
do action 1
do action 2
do action 3
do action 4
do action 5
else
do action 6
do action 7
ENDIF

__________________
-John

Roxy

Ok I see what you mean, so you could place decision within a loop and a loop within one of the steps in a sequence, right. I can understand the psuecode lots better than the flowcharts.
Thank you

jcjacob

yes, that's correct. You're getting it now

That's exactly why I used pseudocode for the examples....it's how I learned and it makes the most sense to me. I only used flowcharts to diagram the highest levels of functionality, much like an outline.

__________________
-John

Roxy

You're right I do understand the examples you gave and my mind is wrapping around it better. Thank you so much.

Roxy

Thanks again John, I made a 95 on the quiz she threw at us yesterday.

jcjacob

That's awesome Roxy - you should be very proud of yourself. I'm happy for you!

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-John