Tuesday, June 30, 2009
FLOWCHARTING
INTRODUCTION
The flowchart is a means of visually presenting the flow of data through an information processing systems, the operations performed within the system and the sequence in which they are performed. In this lesson, we shall concern ourselves with the program flowchart, which describes what operations (and in what sequence) are required to solve a given problem. The program flowchart can be likened to the blueprint of a building. As we know a designer draws a blueprint before starting construction on a building. Similarly, a programmer prefers to draw a flowchart prior to writing a computer program. As in the case of the drawing of a blueprint, the flowchart is drawn according to defined rules and using standard flowchart symbols prescribed by the American National Standard Institute, Inc.
OBJECTIVES
At the end of this lesson, you will be able to understand:
the meaning of flowchart
the basic parts of the flowchart such as flowchart symbols and the flow lines connecting these symbols.
the advantages and limitations of flowchart
MEANING OF A FLOWCHART
A flowchart is a diagrammatic representation that illustrates the sequence of operations to be performed to get the solution of a problem. Flowcharts are generally drawn in the early stages of formulating computer solutions. Flowcharts facilitate communication between programmers and business people. These flowcharts play a vital role in the programming of a problem and are quite helpful in understanding the logic of complicated and lengthy problems. Once the flowchart is drawn, it becomes easy to write the program in any high level language. Often we see how flowcharts are helpful in explaining the program to others. Hence, it is correct to say that a flowchart is a must for the better documentation of a complex program.
GUIDELINES FOR DRAWING A FLOWCHART
Flowcharts are usually drawn using some standard symbols; however, some special symbols can also be developed when required. Some standard symbols, which are frequently required for flowcharting many computer programs are shown in Fig. 25.1
Start or end of the program
Computational steps or processing function of a program
Input or output operation
Decision making and branching
Connector or joining of two parts of program
Magnetic Tape
Magnetic Disk
Off-page connector
Flow line
Annotation
Display
Flowchart Symbols
The following are some guidelines in flowcharting:
In drawing a proper flowchart, all necessary requirements should be listed out in logical order.
The flowchart should be clear, neat and easy to follow. There should not be any room for ambiguity in understanding the flowchart.
The usual direction of the flow of a procedure or system is from left to right or top to bottom.
Only one flow line should come out from a process symbol.
or
Only one flow line should enter a decision symbol, but two or three flow lines, one for each possible answer, should leave the decision symbol.
Only one flow line is used in conjunction with terminal symbol.
Write within standard symbols briefly. As necessary, you can use the annotation symbol to describe data or computational steps more clearly.
If the flowchart becomes complex, it is better to use connector symbols to reduce the number of flow lines. Avoid the intersection of flow lines if you want to make it more effective and better way of communication.
Ensure that the flowchart has a logical start and finish.
It is useful to test the validity of the flowchart by passing through it with a simple test data.
ADVANTAGES OF USING FLOWCHARTS
The benefits of flowcharts are as follows:
Communication: Flowcharts are better way of communicating the logic of a system to all concerned.
Effective analysis: With the help of flowchart, problem can be analysed in more effective way.
Proper documentation: Program flowcharts serve as a good program documentation, which is needed for various purposes.
Efficient Coding: The flowcharts act as a guide or blueprint during the systems analysis and program development phase.
Proper Debugging: The flowchart helps in debugging process.
Efficient Program Maintenance: The maintenance of operating program becomes easy with the help of flowchart. It helps the programmer to put efforts more efficiently on that part
LIMITATIONS OF USING FLOWCHARTS
Complex logic: Sometimes, the program logic is quite complicated. In that case, flowchart becomes complex and clumsy.
Alterations and Modifications: If alterations are required the flowchart may require re-drawing completely.
Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a problem.
The essentials of what is done can easily be lost in the technical details of how it is done.
--------------------------------------------------------------------------------
Quiz!
IN-TEXT QUESTIONS 1
Fill in the blank.
A program flowchart indicates the_________ to be per formed and the __________ in which they occur.
A program flowchart is generally read from _____________ to ________________
Flowcharting symbols are connected together by means of ___________________
A decision symbol may be used in determining the ____________ or ___________ of two data items.
__________ are used to join remote portions of a flowchart
____________ connectors are used when a flowchart ends on one page and begins again on other page
A ________ symbol in used at the beginning and end of a flowchart.
The flowchart is one of the best ways of ________ a program..
To construct a flowchart, one must adhere to prescribed symbols provided by the __________ .
The programmed uses a ____________ to aid him in drawing flowchart symbols.
--------------------------------------------------------------------------------
Algorithm Flowcharts are often used to graphically represent algorithms.In mathematics, computing, linguistics, and related subjects, an algorithm is a finite sequence of instructions, an explicit, step-by-step procedure for solving a problem, often used for calculation and data processing. It is formally a type of effective method in which a list of well-defined instructions for completing a task, will when given an initial state, proceed through a well-defined series of successive states, eventually terminating in an end-state. The transition from one state to the next is not necessarily deterministic; some algorithms, known as probabilistic algorithms, incorporate randomness.
Why algorithms are necessary: an informal definition
For a detailed presentation of the various points of view around the definition of "algorithm" see Algorithm characterizations. For examples of simple addition algorithms specified in the detailed manner described in Algorithm characterizations, see Algorithm examples.
While there is no generally accepted formal definition of "algorithm", an informal definition could be "a process that performs some sequence of operations." For some people, a program is only an algorithm if it stops eventually. For others, a program is only an algorithm if it stops before a given number of calculation steps.
A prototypical example of an "algorithm" is Euclid's algorithm to determine the maximum common divisor of two integers (X and Y) which are greater than one: We follow a series of steps: In step i, we divide X by Y and find the remainder, which we call R1. Then we move to step i + 1, where we divide Y by R1, and find the remainder, which we call R2. If R2=0, we stop and say that R1 is the greatest common divisor of X and Y. If not, we continue, until Rn=0. Then Rn-1 is the max common division of X and Y. This procedure is known to stop always and the number of subtractions needed is always smaller than the larger of the two numbers.
Formalization
Algorithms are essential to the way computers process information. Many computer programs contain algorithms that specify the specific instructions a computer should perform (in a specific order) to carry out a specified task, such as calculating employees’ paychecks or printing students’ report cards. Thus, an algorithm can be considered to be any sequence of operations that can be simulated by a Turing-complete system. Authors who assert this thesis include Savage (1987) and Gurevich (2000):
...Turing's informal argument in favor of his thesis justifies a stronger thesis: every algorithm can be simulated by a Turing machine (Gurevich 2000:1)...according to Savage [1987], an algorithm is a computational process defined by a Turing machine. (Gurevich 2000:3)
Typically, when an algorithm is associated with processing information, data is read from an input source, written to an output device, and/or stored for further processing. Stored data is regarded as part of the internal state of the entity performing the algorithm. In practice, the state is stored in one or more data structures.
For any such computational process, the algorithm must be rigorously defined: specified in the way it applies in all possible circumstances that could arise. That is, any conditional steps must be systematically dealt with, case-by-case; the criteria for each case must be clear (and computable).
Because an algorithm is a precise list of precise steps, the order of computation will always be critical to the functioning of the algorithm. Instructions are usually assumed to be listed explicitly, and are described as starting "from the top" and going "down to the bottom", an idea that is described more formally by flow of control.
So far, this discussion of the formalization of an algorithm has assumed the premises of imperative programming. This is the most common conception, and it attempts to describe a task in discrete, "mechanical" means. Unique to this conception of formalized algorithms is the assignment operation, setting the value of a variable. It derives from the intuition of "memory" as a scratchpad. There is an example below of such an assignment.
For some alternate conceptions of what constitutes an algorithm see functional programming and logic programming .
Algorithms can be expressed in many kinds of notation, including natural languages, pseudocode, flowcharts, and programming languages. Natural language expressions of algorithms tend to be verbose and ambiguous, and are rarely used for complex or technical algorithms. Pseudocode and flowcharts are structured ways to express algorithms that avoid many of the ambiguities common in natural language statements, while remaining independent of a particular implementation language. Programming languages are primarily intended for expressing algorithms in a form that can be executed by a computer, but are often used as a way to define or document algorithms.
There is a wide variety of representations possible and one can express a given Turing machine program as a sequence of machine tables (see more at finite state machine and state transition table), as flowcharts (see more at state diagram), or as a form of rudimentary machine code or assembly code called "sets of quadruples" (see more at Turing machine).
Sometimes it is helpful in the description of an algorithm to supplement small "flow charts" (state diagrams) with natural-language and/or arithmetic expressions written inside "block diagrams" to summarize what the "flow charts" are accomplishing.
7:02 AM
www.kerviiin-oweight.blogspot.com
