Transcript Program Flow Charts

The Program Design Phases
Define the problem
Propose and evaluate solutions
Determine the most efficient
solution
Develop and represent the
algorithm
Test and validate the solution
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 FLOWCHARTS
These 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 most common flowchart
symbols are :
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
START
END
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
Add number to subtotal
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
Input name
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
Yes
Even number ?
No
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
Sort Marks
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.
PROGRAM FLOWCHARTS cont’d
B
A
A
B
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
START
Step 1
Sequence of steps
Step 2
Step 3
END
PROGRAM FLOWCHARTS cont’d
Combining symbols
n = sum + grade
Decision (if statement)
N > 50?
Yes
No
Give
certificate
END
PROGRAM FLOWCHARTS cont’d
Combining symbols
n=n+1
Loops
WHILE loop
( loops involve
a) decisions and
False
branching
{if statements}
b) Returning to
previous
< action continuing
statements
program >
)
N < 50?
True
< an action >
PROGRAM FLOWCHARTS cont’d
Combining symbols
n=n+1
Loops
REPEAT loop
< an action >
In a REPEAT loop the action
takes place before the first check
False
< action continuing
program >
N < 50?
True
Start
Sum = 0
Input price
Sum = sum + price
CASH REGISTER PROGRAM
Yes
More
items?
No
Tax = sum x 0.15
Output sum, tax,
End
Common Flowchart Symbols
Common Flowchart Symbols
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 commands
to 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 with
a flow line in and the other with a flow line out.
Off-page connector. Even fairly small programs can have flowcharts that extend several
pages. 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.
FYI : Other Symbols
------
tape
annotation / notes
disk
display
document
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
Draw Backs of Flowcharts
• When programs are large or
complex, the chart becomes too
complicated
• If alterations are required, the entire
chart may have to be re-drawn
Because of this, the use of program
flowcharts is actually in decline