ALGORITHMS AND FLOWCHART

Algorithms

•         Computing problems

–        Can be solved by executing a series of actions in a specific order

•         An algorithm is

–        A procedure for solving a problem in terms of

•         The actions to be executed, and

•         The order in which these actions are executed

•         Program control is

–        Specifying the order in which statements are to be executed

–         

Pseudocodes

•         A pseudocode is

–        An artificial and informal language that helps programmers develop algorithms

–        Similar to the natural language

–        Not an actual programming language

–        Not actually executed on computers

•         Why do you need it?

–        Helps to “think out” a program before writing it

–        May be converted easily into a corresponding C program

 An Example:

Pseudocode for calculation of grade of students

Input the marls of student

if student’s mark is greater than or equal to 90

     print “A”

else

     if student’s mark is greater than or equal to 80

          print “B”

     else

          if student’s mark is greater than or equal to 70

              print “C”

          else

              if student’s mark is greater than or equal to 60

                   print “D”

              else

                   print “F”

Flowcharts

•         A flowchart is

–        A graphical representation of an algorithm, or of a portion of an algorithm

–        Useful for developing and representing algorithms

–        Drawn using certain special-purpose symbols connected by arrows called flowlines

•         Symbols indicate the actions to be performed, and flowlines indicate the order in which actions are to be performed

Flow chart symbols

Flow chart symbols

                         

Symbol	Description
	Oval symbol (or termination symbol) indicates the beginning or end of a program, or a section of code
	Rectangle symbol (or action symbol) indicates any type of processing, calculation
	Subprocess symbol used for pre-defined process
	Parallelogram symbol For input/output operation
	Diamond symbol (or decision symbol) indicates that a decision is to be made
	Flowline connects one symbol to another
	Entry or exit points are used to attach the one flowchart to another

The flow chart equivalent to the above pseudocode

                                              

Using flow charts to design programs

The algorithm sums all the even numbers between 1 and 20 inclusive and then displays the sum. It uses a repeat loop and contains a null else within the repeat loop.

The equivalent pseudocode is: 

1. sum = 0 
2. count = 1 
3. REPEAT 
   IF count is even THEN

 sum = sum +  count 
   count = count + 1 
   UNTIL count >20 
4. DISPLAY sum

We can see quite clearly from this example what the price of flow charting is. There is quite a bit of drawing to do in addition to writing the legend in the symbols. The pseudocode is quite simple by comparison so why would you use flow charts?

The major reasons are that the flow chart.

• is easier to read
• more closely follows a standard, this is not the the case with pseudocode
• easier to understand than pseudocode

We can see quite clearly from this example what the price of flow charting is. There is quite a bit of drawing to do in addition to writing the legend in the symbols. The pseudocode is quite simple by comparison so why would you use flow charts?

The major reasons are that the flow chart.

• is easier to read
• more closely follows a standard, this is not the the case with pseudocode
• easier to understand than pseudocode