Chapter 8
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DISPLAY OF CYCLES
The success of a decision depends on the person's ability to
"visualize the problem situation", visualize it and operate
visual images.
Natalia Zavalova Boris Lomov,
Vladimir Ponomarenko
NORMAL CYCLE
In the language of DRAGON has the following range of cycles:
* ordinary cycle;
* switching cycle;
* FOR loop;
* twig cycle;
* loop wait.
The first four-cycle considered in this chapter, the cycle of
wait - in Ch. Eleven.
The composite visual operator "normal cycle" (Fig. 2, makroikona
4) contains icons of "question" and "loop the loop" (Fig. 1,
icons I4, I24). It covers the three types of cycles (Fig.
34-36):
* cycle to (do-while),
* WHILE loop (while-do),
* Hybrid cycle (do-while-do).
Examples cycles to repent and are shown in Fig. 37, 38. Early
exit from the cycle shown in Fig. 39-42. Construction "loop
cycle" shown in Fig. 43-45.
Analyzing the figures, you will notice the following features.
* Operator "normal cycle" has one input and one or more
outlets.
* Cycle single output represents skewer block (input and
output are in the same vertical).
* If the cycle has more than one exit, the main exit is
located on the main vertical extra - the right of it.
* Loop the loop is to the right of the main vertical and
twisted counterclockwise.
* Icon "issue" sets the loop condition, which is divided into
two parts: the conditions of continuation and termination
condition (Fig. 37).
* Condition corresponds to the continuation of the right
output icon "question", the termination condition - lower.
* The condition can be marked as the end of the word "no" and
the word "yes." The same applies to extension condition.
SWITCH and switch CYCLE
Suppose the algorithm need to organize branching into several
directions. The problem can be solved in two ways: using the
icons "issue" (Fig. 46a) and a switch (Fig. 46b).
Switch - a visual component operator (Fig. 2, the macro icon 3)
having one input and one output, having one icon of "choice" and
a few (two or more) icons "option" (Fig. 1, icons I5, u6) .
Inside icon "choice" is the inscription, usually in the
affirmative, which represents an issue of strictly defined
number of responses (two or more). Answers written in icons
"option." Thus, the number of options equal to the number of
responses. Formally speaking, the icon in the "choice" written
variable in the icons "option" - its values. Fig. 46b variable
"Traffic Light" takes three values: green, yellow, red.
The switch allows you to create a special type of cycle -
switching cycle (Fig. 2, makroikona 5). To do this, pull the
right arm of the output switch, bend it up and connect the arrow
to the right place (Fig. 47).
Fig. 48 shows a cycle with a switch, but it is not the switching
cycle, and the usual. How to tell them apart? In the first case,
the switch has two outputs, the second - only one. There is
another difference. If output is curled upward Icons "issue" -
it is a regular cycle (DO WHILE, or hybrid). If the output
switch is up - we are switching cycle.
CYCLE FOR
Fig. 49 and 50 show two options to solve a simple problem
matemati*cheskoy. In the first case, a cycle before, the second
- cycle for. Cycles for - visual component operator (Fig. 2, the
macro icon 6) containing the icon "start cycle for" and "end of
cycle for" (Fig. 1, the icons and 12, and 13), between which one
or more other icons. Inside icon "start cycle for" indicates the
loop variable, its initial and final value and the step. The
procedure for recording these values ??determined by the
selected text option syntax. Fig. 50 illustrates an embodiment,
the default is that the pitch is equal to 1.
Twig CYCLE
Rings described above can be used in both primitive and in
silhouette. In this section we will focus on twig cycle, which
occurs only in silhouette.
Twig cycle is generated when the label is in the icon of the
"address" indicates either a branch, or a branch, which is to
the left. For example, the icon of the address "Buying buns" in
Fig. 51 points to his branch. Within the cycle of browse may
appear cycles of other types. Fig. 52 shows the construction of
the "cycle in the loop", which is located inside of browse cycle
to cycle.
When replacing the primitive to the equivalent silhouette hybrid
cycle often turns into a twig cycle. This is easily seen by
comparing the equivalent algorithms in Fig. 41 and 53.
The main route SILHOUETTE
In this section we continue the study of cycles twig and try to
answer the question: how to find the main route of browse cycle?
To do this, you need to analyze the concept of "the main route
silhouette" (Fig. 54).
Linear (straight) has a silhouette of a single route, which is
the main thing. He passes on a skewer all branches and all the
icons silhouette (Fig. 54a).
The formula for the route silhouette has a singularity: the icon
of the same name "address" and "branch name" refers to a single
letter, which is repeated twice in the formula. For example, a
silhouette in Fig. 54a has the formula
ABEFGC - CHID - DJKM
where the paired letters denote the transition from the first to
the second branch (C - C) and the second to the third (D - D).
The branch is called unicast, if it has one icon "address". If
all branches unicast silhouette considered unicast.
Line silhouette always unicast. However, unicast silhouette can
be branched. In the latter case, its main route follows the
skewer all the branches, but it does not go all the icons (Fig.
54b).
If at least one branch has more than one address, it may be a
situation where some branches do not fall on the main route.Fig.
54B icon address D is for side route. This leads to the fact
that the branch D is also provided on the secondary route.As a
result, the main route passes through the skewer all the
branches, except branch D (Fig. 54B).
Twig loops are formed only in multicast silhouettes, one-address
them, in principle, can not be. They come in several types:
* odnovetochnye (if the loop is placed in one branch);
* dvuhvetochnye (if the cycle takes two branches);
* trehvetochnye (cycle in three branches), and so on. d.
How does odnovetochny cycle? Assume before the loop in Fig. 54g
that the conditions
Assume also that the twig cycle performed twice, after which the
condition E is set to "no." This means that the third pass of
the branch in the loop will exit the path "E No C". In such a
situation, the formula of the main route for the silhouette in
Fig. 54g takes the form:
What is the main route to the dragon scheme? Response shows a
thick line in Fig. 54g. We see that the main route as it
branches out in the icon E and passes through both of its
release. Of course, this convention, which means the
following.At first (when E = yes) the main route is on a skewer,
and then (when the condition E = end of the cycle is not) main
route passes through the right output icon E.
To build odnovetochny cycle, you need the left icon "address"
record X, where X - the name of the branch. To exit the loop
should add a second icon of the "address" and write in it Y,
where Y - the name of the following (in order of performance)
branches.
If the twig cycle too many icons, it may not fit in one branch.
Fortunately, it can be divided into parts. For example, a twig
cycle in Fig. 54d has five icons: E, F, G, H, R (icon "branch
name" and "address" does not count). Put icons E and F in branch
B, and the icon G, H, R - in the branch C. As a result, the
cycle will dvuhvetochnym. The main route silhouette with
dvuhvetochnym cycle has a branch in the icon condition R. R =
yes lets go back to the top of the cycle. R = If not, the main
route leads us to the end of the algorithm (Fig. 54d).
Thus dvuhvetochny cycle - a cycle comprising two threads X and
Y, wherein X is a branch icon address Y, and branch Y - icon
address X.
Fig. 54e shows the situation "cycle in the loop": the cycle C is
a twig of browse inside the loop B. It can be seen that in this
case the main route "branches" twice in the icons and R J.
If the condition R = yes, there is a repetition of the inner
loop C. When combined conditions
R = No J = Yes
made out of the loop and repeat With the outer loop B. Finally,
a combination of conditions
R = No J = No
It means that the loop B and the whole algorithm ends.
CONCLUSIONS
1. In various text languages ??in the description of cycles
used different sets of keywords relevant to the different
semantics. Confusion exacerbate differences in logic end of
the cycle. For example, in C language for while loops, and
do-while loop termination condition corresponds to false or
0, the continuation condition - true or 1. Pascal picture is
different: in a loop while-do out of the cycle corresponds
to the value false, and the cycle repeat-until, for some
mysterious reasons applied diametrically opposite principle:
a way out of the cycle is when the logical expression
evaluates to true. All these confusing the programmer must
know the rules and to abide scrupulously.
2. The lack of unification of keywords and inconsistency in the
definition of the conditions out of the loop is a serious
drawback: the programmers have to cram keywords and value
terms, and development of each of the following new language
requires cramming.
3. In terms of visual programming, these difficulties are
far-fetched and easily eliminated. We only need to abandon
existing habits and outmoded stereotypes of thinking
associated with textual programming. Visualization of a
qualitative change in the situation, since the text is no
longer the only carrier of information.
4. Visual images reduce the burden on the programmer's memory,
eliminate errors caused by misunderstanding of the semantics
of the keywords cancel unnecessary restrictions, provide the
user with a rich palette of expressive means and ultimately
provide greater comprehensibility of algorithms and
programs.
5. Visualization of the cycle - a very useful tool as
complicated nested loops with many outlets are often the
source of errors difficult. Many of them arise from the
confusion associated with outdated habit to describe the
cycles of the words. Today, no one is trying to replace the
design and construction drawings, verbal descriptions.
According to the author, the text form of the cycles in many
cases is as anachronistic as a verbal description of a
mechanical drawing, or circuitry.
References
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