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The Program Design Phases
Propose and evaluate solutions
Determine the most efficient solution
Develop and represent the algorithm
Test and validate the solution
Define the problem
Programs are Solutions to Problems
Programmers can represent their solutions in several ways :
• Structure Charts• Pseudocode• Flowcharts
These are the tools used in structured programming
Structured Programming
• Structured program languages lend themselves to flowcharts, structure charts, and pseudocode.
• Structured programming languages work best where the instructions have been broken up into small, manageable parts (procedures/modules).
Pseudocode
• This device is not visual but is considered a “first draft” of the actual program.
• Pseudocode is written in the programmer’s native language and concentrates on the logic in a program — not the syntax of a programming language.
Flowcharts
A flowchart is a pictorial representation of all the steps in a process.( A picture is worth a 1000 words )
There are Block flowcharts,System flowcharts,Procedure flowcharts and Program flowcharts
PROGRAM FLOWCHARTSThese represent the flow of logic in a
program and help programmers “see” program design. They are also sometimes called logic flowcharts.
Flow charts are drawn in the design phase of programming.
A flowchart is comprised of specialised symbols and flow lines. Each symbol contains information about what must be done at that point; and the arrow shows the flow of execution.
PROGRAM FLOWCHARTS cont’d
… show the step by step sequence of operations carried out by a computer program
the start and end of the program the input and output operations how the data is processed the main sections of the program
Program flowcharts should be sufficiently detailed for the program code to be written directly from it, making it, therefore, just like pseudocode
PROGRAM FLOWCHARTS cont’d
The start / end symbol
Each flowchart must begin and end with the terminator symbol. The word START or END is
written inside the oval
PROGRAM FLOWCHARTS cont’d
The process symbol
This indicates an operation such as a calculation Details are written in the rectangle and should
begin with a verb
PROGRAM FLOWCHARTS cont’d
The input / output symbol
This marks the point at which we get data or give results. The input or output is written inside the
parallelogram.
PROGRAM FLOWCHARTS cont’d
The decision symbol
This is used where a decision has to be made in selecting the subsequent path to be followed. Note that while there is only one entry point to
the diamond there are at least 2 exits
PROGRAM FLOWCHARTS cont’d
The pre-defined process symbol
This is used to represent a process which is broken down elsewhere
PROGRAM FLOWCHARTS cont’d
The connector symbols
Connector
Off-page connector
These are used to break and continue links without crisscrossing lines all over the place. So
they link with another part of the program or another page.
Drawing Flow Charts
• Organize the flowchart in modules
• Use standard symbols only, you can vary the size
but not the shape
• Try to keep the logic as flowing from top to bottom
and from left to right
• Do not cross flow lines
• Use a template if possible
• Add notes if necessary for clarity but not not clutter
PROGRAM FLOWCHARTS cont’d
Combining symbols
Decision (if statement)
n = sum + grade
N > 50?
Give certificate
END
YesNo
PROGRAM FLOWCHARTS cont’d
Combining symbols
Loops WHILE loop
( loops involve
a) decisions and branching {if statements} b) Returning to previous statements )
n = n + 1
N < 50?
< an action >
True
< action continuing program >
False
Combining symbols
Loops REPEAT loop
In a REPEAT loop the action
takes place before the first check
PROGRAM FLOWCHARTS cont’d
n = n + 1
N < 50?
< an action >
True < action continuing program >
False
Start
Sum = 0
Input price
Sum = sum + price
Moreitems?
Tax = sum x 0.15
Output sum, tax,
End
No
Yes
CASH REGISTER PROGRAM
Terminator. Shows the starting and ending points of the program. A terminator has flow lines in only one direction, either in (a stop node) or out (a start node).
Data Input or Output. Allows the user to input data and results to be displayed.
Processing. Indicates an operation performed by the computer, such as a variable assignment or mathematical operation.
Decision. The diamond indicates a decision structure. A diamond always has two Flow lines out. One flow line out is labeled the “yes” branch and the other is labeled the “no” branch.
Predefined Process. One statement denotes a group of previously defined statements. For instance, “Calculate m!” indicates that the program executes the necessary commandsto compute m factorial.
Connector. Connectors avoid crossing flow lines, making the flowchart easier to read. Connectors indicate where flow lines are connected. Connectors come in pairs, one witha flow line in and the other with a flow line out.
Off-page connector. Even fairly small programs can have flowcharts that extend severalpages. The off-page connector indicates the continuation of the flowchart on another page. Just like connectors, off-page connectors come in pairs.
Flow line. Flow lines connect the flowchart symbols and show the sequence of operations during the program execution.
Common Flowchart Symbols
Common Flowchart Symbols
Benefits of Flowcharts
• Communication : a better way of communicating because they are visual
• Effective analysis : the visual nature allows quick grasp of program logic
• Aids in technical documentation
• Good guide when it is time to code
• Good aid when program maintenance becomes necessary