9.2 AlgDesign.algorithms

Question 1

What is Structured English in algorithm design?

Answer 1

A method of showing logical steps in an algorithm using straightforward English words for commands and mathematical operations.

Question 2

What is a flowchart?

Answer 2

A diagrammatic representation of an algorithm, using symbols and flow lines to show the steps and their order.

Question 3

What is an algorithm?

Answer 3

An ordered set of steps to be followed for completing a task.

Question 4

What is pseudocode?

Answer 4

A representation of the logical steps in an algorithm using keywords, meaningful identifiers, and mathematical operators without adhering to a specific programming language’s syntax.

Question 5

What is stepwise refinement?

Answer 5

The practice of breaking down a larger problem into smaller, manageable parts, and further subdividing them as needed. In program development, breaking down each step into smaller processes.

Question 6

What are three common methods for writing algorithms?

Answer 6

1. Structured English: Logical steps in plain English.
2. Flowchart: Diagrammatic representation of the steps.
3. Pseudocode: Detailed logical steps with keywords and operators.

Question 7

What are the key features of Structured English?

Answer 7

• Uses simple English commands.
• Represents logical steps clearly.
• Often includes numbering for each step.

Question 8

Why are flowcharts effective in algorithm design?

Answer 8

They visually represent the structure of an algorithm, showing the sequence and relationships between steps.

Question 9

How does pseudocode help in programming?

Answer 9

• Provides sufficient detail for writing programs in high-level languages.
• Uses meaningful names and logical steps.
• Avoids the syntax constraints of specific programming languages.

Question 10

Example of Structured English Algorithm:

Answer 10

1 Ask for the number of values
2 Loop that number of times
3 Enter a value in the loop
4 Add the value to the total in the loop
5 Calculate and output the average

Question 11

How is each step in a pseudocode algorithm typically written?

Answer 11

Each line of pseudocode represents a single step in the algorithm.

Question 12

How should identifiers in pseudocode be written?

Answer 12

• Use meaningful names, such as Name for a person’s name.
• Identifiers should only contain characters A–Z, a–z, and 0–9.
• Start identifiers with a letter.
• They are case-insensitive.

Question 13

What can be used to track identifiers used in pseudocode?

Answer 13

A pseudocode table, with the Identifier name and Description for each identifier. This helps maintain clarity and organisation.

Question 14

How do you input a value in pseudocode?

Answer 14

Use the INPUT statement:

Syntax:
INPUT <Identifier>
Example:
INPUT StudentName

Question 15

How do you output a message, value, or combination in pseudocode?

Answer 15

Use the OUTPUT statement:

Syntax:
OUTPUT <…>
Examples:
OUTPUT "You have made an error”
OUTPUT StudentName
OUTPUT "Student name is ", StudentName

Question 16

How do you assign a value to a variable in pseudocode?

Answer 16

Use the ‘<Identifier> ← <value>' statement.</value></Identifier>

Examples:

Counter ← 1
Counter ← Counter + 1
MyChar ← “A”
LetterValue ← ASC(MyChar)
StudentMark ← 40
Percentage ← (StudentMark / 80) * 100

Question 17

How can you concatenate strings in pseudocode?

Answer 17

Use the & operator for concatenation.
Example:

OldString ← "Your mark is”
NewString ← OldString & " ninety-seven”

Question 18

What are the operators used in assignment statements in pseudocode?

Answer 18

+: addition
-: subtraction
*: multiplication
/: division
&: string concatenation
←: assignment

Question 19

How do you write an IF statement for a single choice in pseudocode?

Answer 19

IF <Condition> 
    THEN
        <Action>
ENDIF

Example:

IF MyValue > YourValue 
    THEN
        OUTPUT "I win"
ENDIF

Question 20

How do you write an IF statement with a single choice and an alternative in pseudocode?

Answer 20

IF <Condition> 
    THEN
        <Action>
    ELSE
        <Alternative Action>
ENDIF

Example:

IF MyValue > YourValue 
    THEN
        OUTPUT "I win"
    ELSE
        OUTPUT "You win"
ENDIF

Question 21

How do you write a CASE statement for multiple choices in pseudocode?

Answer 21

CASE OF <Variable>
    "Choice1": <Action1>
    "Choice2": <Action2>
    ...
ENDCASE

Example:

CASE OF Direction
    "N": Y ← Y + 1
    "S": Y ← Y – 1
    "E": X ← X + 1
    "W": X ← X – 1
ENDCASE

Question 22

How do you write a CASE statement with an alternative in pseudocode?

Answer 22

CASE OF <Variable>
    "Choice1": <Action1>
    "Choice2": <Action2>
    ...
    OTHERWISE: <Alternative Action>
ENDCASE

Example:

CASE OF Direction
    "N": Y ← Y + 1
    "S": Y ← Y – 1
    "E": X ← X + 1
    "W": X ← X – 1
    OTHERWISE: OUTPUT "Error"
ENDCASE

Question 23

What are the relational operators in pseudocode?

Answer 23

=: Equal to
<>: Not equal to
>: Greater than
>: Less than
>=: Greater than or equal to
<=: Less than or equal to

Question 24

How is a single-choice IF statement constructed in Python?

Answer 24

A colon : starts the THEN clause, and all statements in the THEN clause are indented.

Example:

myValue = int(input("Please enter my value "))
yourValue = int(input("Please enter your value "))
if myValue > yourValue: 
    print("I win")

Question 25

Example for a FOR loop with a fixed number of repetitions in pseudocode

Answer 25

``` Total ← 0 FOR Counter ← 1 TO 10 OUTPUT "Enter a number " INPUT Number Total ← Total + Number NEXT Counter OUTPUT "The total is ", Total ```

Question 26

What is the purpose of the STEP increment in a FOR loop in pseudocode?

Answer 26

It specifies an optional step size for the counter, which must be a whole number.

Question 27

Example of a FOR loop with a STEP increment in pseudocode

Answer 27

``` FOR Counter ← 1 TO 10 STEP 2 OUTPUT Counter NEXT Counter ```

Question 28

How does a REPEAT–UNTIL loop function in pseudocode?

Answer 28

A REPEAT loop always executes its statements at least once and repeats until a specified condition is true. Example: ``` REPEAT OUTPUT "Please enter a positive number " INPUT Number UNTIL Number > 0 ```

Question 29

How does a WHILE loop function in pseudocode?

Answer 29

A WHILE loop checks its condition before execution and may not execute at all if the condition is false initially. Example: ``` Number ← 0 WHILE Number >= 0 DO OUTPUT "Please enter a negative number " INPUT Number ENDWHILE ```

Question 30

Python example of a FOR loop with a step increment

Answer 30

``` for Counter in range(1, 10, 2): print(Counter) ```

Question 31

How does a REPEAT–UNTIL loop ensure a statement is executed at least once?

Answer 31

The condition is evaluated *after* the execution of the loop's body. Example: ``` REPEAT OUTPUT "Please enter a positive number less than fifty" INPUT Number UNTIL (Number > 0) AND (Number < 50) ```

Question 32

What logic operators are used in pseudocode?

Answer 32

`AND`: Both conditions must be true. `OR`: At least one condition must be true. `NOT`: Inverses the truth value of a condition.

Question 33

What function can be used to return the integer value of a variable in pseudocode?

Answer 33

`INT(x)`

Question 34

Write a program in pseudocode for finding the average of a set of integers with input validation

Answer 34

``` Total ← 0 REPEAT PRINT "Enter the number of values to average" INPUT Number UNTIL (Number > 0) AND (Number = INT(Number)) FOR Counter ← 1 TO Number REPEAT PRINT "Enter an integer value " INPUT Value UNTIL Value = INT(Value) Total ← Total + Value NEXT Counter Average ← Total / Number PRINT "The average of ", Number, " values is ", Average ``` identifier table for the algorithm: Total: Running total of integer values entered Number: Number of integer values to enter Value: Integer value input Average: Average of all the integer values entered

Question 35

Write a program in Python for finding the average of a set of integers with input validation. How is it different from the one in pseudocode?

Answer 35

# Find the average of a number of integers input Python ``` Total = 0 Number = int(input("Enter the number of values to average ")) while Number <= 0: Number = int(input("Enter the number of values to average ")) # An extra input is needed, as a WHILE loop must be used for Counter in range(1, Number + 1): Value = int(input("Enter an integer value ")) Total += Value Average = Total / Number print("The average of", Number, "values is", Average) ``` - Python lacks a `REPEAT–UNTIL` construct, requiring a `WHILE` loop to validate the input before proceeding. - The `range()` function is used, and the loop **ends before the final value is reached**, so `range(1, Number + 1)` is used to include the last value.

Question 36

What are the flowchart symbols and their purposes?

Answer 36

Parallelogram: INPUT or OUTPUT operations. Rhombus: decision-making constructs like IF, CASE, or parts of FOR, REPEAT, and WHILE loops. Rectangle: assignment, calculations, or predefined processes (e.g., INT). Obround: (start and end) terminators. Returning flow line: iterative constructs like FOR, REPEAT, and WHILE loops.