Fundamentals of Programming
Topic 1 : Introduction to Problem Solving Topic 2 : Program Design
Content
• IPO Model
• Algorithm
• Pseudocode
• Sequence
• Selection control
• Repetition control
• Flowchart
• Sequence
• Selection control
• Repetition control
• Desk checking
Learning Outcomes
By the end of this session, you should be able to
• Produce the IPO model defining the input, output and processes of a solution in response to problems posed.
• Write the pseudocode to solve various problems posed.
• Perform desk checking for the algorithm.
• Define the problem – Input / Output
• Outline the solution – Process (IPO)
• Develop the outline into an algorithm – Pseudocode & Flowchart
• Test the algorithm for correctness – Desk checking
• Code the algorithm into a specific programming language
• Run the program on the computer
• Document and maintain the program
Program
Development
Cycle
IPO model
Input Processing Output
IPO model
Sample Question 1:
Design a program that allows the user to enter values for the width and length of a room’s floor in feet. The program outputs the area of the floor in square feet. The program should also then compute and output the number of 12-inch square tiles needed to tile the floor.
Six basic computer operations
•A computer can receive information (READ, GET)
•A computer can put out information (DISPLAY, PRINT)
•A computer can perform arithmetic (+, -, *, /, %)
•A computer can assign a value to a variable or memory location (height = 150) (area = length * width)
•A computer can compare two variables and select one of two alternative actions (if statement, switch statement)
•A computer can repeat a group of actions (while loop, do…while loop, for loop)
Algorithm
• Lists the steps involved in accomplishing a task
• a set of detailed, unambiguous and ordered
instructions developed to describe the processes
necessary to produce the desired output from a given input
• Is written in simple English
• Can be defined in programming terms
• Popular ways of representing algorithm
• Pseudocode
• Flowchart
Three basic control
structures
Sequence
• Straight forward execution of one processing step after another
• Each instruction will be executed in the order in which it appears
Selection
• Presentation of a condition and the choice between two actions, the choice depending on whether the condition is true or false
• Represents the decision making abilities of the computer
Repetition
• Presentation of a set of instructions to be performed repeatedly as long as a condition is true (until a terminating condition occurs)
• Intialising and subsequent incrementing of the variable tested in the condition is an essential feature
Pseudocode
• Is structured English
• Formalised and abbreviated to look like the high-level computer languages
• There is no standard pseudocode
• Authors adopt their own special techniques and sets of rules – that resemble a particular
programming language
Selection Control
• Represents the decision making abilities of a computer
• To illustrate a choice between two or more actions depending on whether a condition is true or false
• The condition in the IF statement is expressed using either relational operators or equality operators
Operators used in conditions
Relational Operator Meaning
< Less than
> Greater than
< = Less than or equal to
> = Greater than or equal to
Equality Operator Meaning
== Equals to
<> Not equals to
Simple Selection
(Simple IF statement)
Simple Selection with null false branch
(null ELSE statement)
Combined Selection
(Combined IF statement)
IF (condition_1) AND (condition_2) THEN action if both conditions are true
ELSE
action if either one or both conditions are false ENDIF
Condition_1 Condition_2 (Condition_1) AND (Condition_2)
TRUE TRUE TRUE
TRUE FALSE FALSE
FALSE TRUE FALSE
FALSE FALSE FALSE
Combined Selection (Combined IF
statement)
Combined Selection
(Combined IF statement)
IF (condition_1) OR (condition_2) THEN
action if either one or both conditions are true ELSE
action if both conditions are false ENDIF
Condition_1 Condition_2 (Condition_1 )OR (Condition_2)
TRUE TRUE TRUE
TRUE FALSE TRUE
FALSE TRUE TRUE
FALSE FALSE FALSE
Combined Selection (Combined IF
statement)
Combined Selection (Combined IF
statement)
IF NOT(condition) THEN
action if the NOT(condition) result is false ELSE
action if the NOT(condition) result is true ENDIF
Condition NOT (Condition)
TRUE FALSE
FALSE TRUE
Combined Selection (Combined IF
statement)
Nested Selection (nested IF
statement)
• Linear nested IF statements – one variable to compare
IF (condition_1) THEN
action if condition_1 is true ELSE
IF (condition_2) THEN
action if condition_ 1 is false but condition_2 is true ELSE
IF (condition_3) THEN
action if condition_1 and condition_ 2 are false but condition_3 is true ELSE
action if condition_1, condition_2 and condition_3 are false ENDIF
ENDIF ENDIF
Nested Selection (nested IF
statement)
• Non-linear nested IF statements – many variables to compare
IF (condition_1) THEN IF (condition_2) THEN IF (condition_3) THEN
action if condition_1, condition_ 2 and condition_3 are true ELSE
action if condition_1 and condition_2 are true but condition_3 is false ENDIF
ELSE
action if condition_1 is true but condition_2 is false ENDIF
ELSE
action if condition_1 is false ENDIF
CASEOF Structure
CASEOF (variable)
value_1 : statement block_1 value_2 : statement block_2
value_n : statement block_n other : statement block_other ENDCASE
Looping structure
• Will cause the processing logic to be repeated a number of times
• 3 ways the instructions can be repeated
• A counted number of times (counted loop)
• At the beginning of the loop (leading decision loop)
• At the end of the loop (trailing decision loop)
A counter-
controlled loop
• Occurs when the exact number of loop iterations is known in advance
• DOWHILE … ENDDO structure
• LOOP … FROM … TO … STEP… structure
DOWHILE structure
(min to max)
INITIALISE counter as minValue DOWHILE (counter <= maxValue)
Action while the condition is true INCREMENT counter
ENDDO
Action while the condition is false
DOWHILE structure
(max to min)
INITIALISE counter as maxValue DOWHILE (counter >= minValue)
Action while the condition is true DECREMENT counter
ENDDO
Action while the condition is false
LOOP … FROM … TO
…structure (min to max)
LOOP variable FROM minValue TO maxValue STEP increment_value Action
ENDLOOP
LOOP … FROM … TO
…structure (max to min)
LOOP variable FROM maxValue TO minValue STEP decrement_value Action
ENDLOOP
A leading
decision loop
• DOWHILE … ENDDO structure
• The condition is tested before any statements are executed
• Counter controlled (as seen before this)
• Sentinel controlled
DOWHILE…ENDDO structure
(Sentinel controlled)
PROMPT user for initial value (provide the sentinel value) READ value
DOWHILE (value <> sentinel_value) Action while condition is true
PROMPT user for next value (provide the sentinel value) READ value
ENDDO
Action when condition above is false
DOWHILE…
ENDDO structure (Sentinel
controlled)
BEGIN
DISPLAY “Do you want to begin? (Y – to continue /N – to end)”
READ choice
DOWHILE (choice =‘Y’) OR (choice =‘y’) DISPLAY “Desmond is smart”
DISPLAY NEWLINE
DISPLAY “Do you want to continue? (Y – to continue /N – to end)”
READ choice ENDDO
DISPLAY “GoodBye”
END
A trailing decision loop
• REPEAT … UNTIL structure
• The condition is tested at the end of the loop
• Statements within the loop will be executed once before the condition is tested
• When the condition is false, the statements will be executed until the condition is true
• Is opposite of DOWHILE…ENDDO structure
• Normally has an IF statement within
A trailing decision loop
REPEAT
PROMPT user for value (provide sentinel_value) READ value
IF (value <> sentinel_value) THEN
Action is executed only if condition is true ENDIF
UNTIL (value = sentinel_value)
A trailing decision loop
BEGIN REPEAT
DISPLAY “Do you want to run program? (Y or N)”
READ choice
IF (choice<> ‘N’) OR (choice<> ’n’) THEN DISPLAY “You are all smart”
ENDIF
UNTIL (choice = ‘N’) OR (choice = ‘n’) DISPLAY “Goodbye”
END
Desk checking
• Checking the solution algorithm
• Tracing through the logic of the algorithm with some chosen data
