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TEL 104 / MKK Fundamental Programming:

Lecture 4

Calculate_mowing_time1 Prompt operator for block_lenght, block_width2 Get block_length, block_width3 block_area = block_lenght*block_width4 Prompt operator for house_lenght, house_width5 Get house_lenght, house_width6 house_area=house_lenght*house_width7 Mowing_area=block_area-house_area8 Mowing_time=mowing_area/29 Output mowing_time to screen

END

Assignment 2 Review:

Desk Checking

1. Input data:

Data Set 1 Data Set 2

Block_lenght 30 40

Block_widht 30 20

House_lenght 20 20

House_width 20 10

2. Expected result:

Data Set 1 Data Set 2

Mowing_time 250 minutes 300 minutes

3. Set up a table of relevant variable names, and pass each test data set statement by statement.

Statement number

Block_lenght Block_width House_lenght House_width Block_area

House_area Mowing_area

Mowing_time

First Pass

1,2 30 30

3 900

4,5 20 20

6 400

7 500

8 250

9 Output

Second Pass

1,2 40 20

3 800

4,5 20 10

6 200

7 600

8 300

9 Output

4. Check the expected results match the actual results.

Assignment 3 Review:

Calculate_mowing_time1 Prompt operator for block_lenght, block_width2 Get block_length, block_width3 block_area = block_lenght*block_width4 Prompt operator for house_lenght, house_width5 Get house_lenght, house_width6 house_area=house_lenght*house_width7 Mowing_area=block_area-house_area8 Mowing_time=mowing_area/29 Output mowing_time to screen

END

Desk Checking

1. Input data:

Data Set 1 Data Set 2

Block_lenght 30 40

Block_widht 30 20

House_lenght 20 20

House_width 20 10

2. Expected result:

Data Set 1 Data Set 2

Mowing_time 250 minutes 300 minutes

3. Desk Check Table

Statement number

Block_lenght Block_width House_lenght

House_width

Block_area House_area Mowing_area

Mowing_time

First Pass

1,2 30 30

3 900

4,5 20 20

6 900

7 0

8 0

9 Output

Second Pass

1,2 40 20

3 800

4,5 20 10

6 800

7 0

8 0

9 Output

4. Check the expected results match the actual results.

• We found that:– The calculation for the house_area is

incorrect, the result is zero, which cannot be right.

– The algorithm needs to be adjusted:house_area=block_lenght * block_width

– Is changed to:house_area=house_lenght * house_width

Selection Control Structures

Relational Expression

< less than

> greater than

= equal to

<= less than or equal to

>= greater than or equal to

<> not equal to

1. Simple Selection (Simple IF statement)

Keywords: IF, THEN, ELSE, ENDIF

Example:IF account_balance < $300 THEN

service_charge = $5.00

ELSE

service_charge = $2.00

ENDIF

2. Simple Selection with null false branch (null ELSE statement)

Example:

IF student_attendance = part_time THEN

add 1 to part_time_count

ENDIF

3. Combined Selection (Combined IF statement)

• Operator used: AND and OR

• AND both condition must be true

• Example:IF student_attendance = part_time

AND student_gender = female THEN

add 1 to female_part_time_count

ENDIF

Combined Selection (Cont)

• OR only one can be true

• Example:IF student_attendance = part_time

OR student_gender = female THEN

add 1 to female_part_time_count

ENDIF

Combined Selection (Combined IF statement)

• Both operators used• If both operators are used, parentheses

must be used to avoid ambiguity.• Example:

IF record_code = ´23´OR update_code = deleteAND account_balance = zero THEN

delete customer recordENDIF

Combined Selection (Cont)

• Avoid the ambiguity by:IF (record_code = ´23´

OR update_code = delete)

AND account_balance = zero THEN

delete customer record

ENDIF

Combined Selection (Cont)

NOT Operator

• Example:

IF NOT (record_code = ´23´) THEN

update customer record

ENDIF

• Example with AND and OR operator:IF NOT (record_code = ´23´

AND update_code = delete) THEN

update customer record

ENDIF

4. Nested Selection (nested IF statement)

A. Linear Nested IF statements

If record_code = `A´ THEN increment counter_AELSE IF record_code = ´B´ THEN increment counter_B ELSE

IF record_code = ´C´ THEN increment counter_C

ELSE increment error_counterENDIF

ENDIFENDIF

B. Non-linear nested IF statements

IF student_attendance = part_time THENIF student_gender = female THEN

IF student_age > 21 THENadd 1 to mature_female_pt_students

ELSEadd 1 to young_female_pt_students

ENDIFELSE

add 1 to male_pt_studentsENDIF

ELSEadd 1 to full_time_students

ENDIF

IF possible, replace a series of non-linear nested IF statements with a combined IF statements.

IF student_attendance = part_time THENIF student_age > 21 THEN

increment mature_pt_studentsENDIF

ENDIF

IF student_attendance = part_timeAND student_age > 21 THENincrement mature_pt_student

ENDIF

Algorithms Using Selection

Example 4.1 Read three characters

• Design an algorithm that will prompt a terminal operator for three characters, accept those characters as input, sort them into ascending sequence and output them to the screen.

• Defining diagram

Input Processing Output

Char_1Char_2Char_3

Prompt for charactersAccept three charactersSort three charactersOutput three characters

Char_1Char_2Char_3

Solution AlgorithmRead_three_characters

1 Prompt the operator for char_1, char_2, char_32 Get char_1, char_2, char_33 IF char_1 > char_2 THEN

temp = char_1char_1 = char_2char_2 = temp

ENDIF4 IF char_2 > char_3 THEN

temp = char_2char_2 = char_3char_3 = temp

ENDIF5 IF char_1 > char_2 THEN

temp = char_1char_1 = char_2char_2 = temp

ENDIF6 Output to the screen char_1, char_2, char_3

END

Desk Checking

Data Set 1 Data Set 2

Char_1 K Z

Char_2 B S

Char_3 G A

1. Input Data

Data Set 1 Data Set 2

Char_1 B A

Char_2 G S

Char_3 K Z

2. Expected Result

3. Desk Check Table

Statement number

Char_1 Char_2 Char_3 temp

First Pass

1,2 k b g

3 b k k

4 g k k

5

6 output output Output

Second Pass

1,2 z s a

3 s z z

4 a z z

5 a s s

6 output output output

Example 4.2 Process Customer Record

A program is required to read a customer‘s name, a purchase amount and a tax code. The tax code has been validated and will be one of the following:

0 baby needs tax (0%)1 Vegetables and food tax (3%)2 drink sales tax (5%)3 special sales tax (7%)

The program must then compute the sales tax and the total amount due, and print the customer‘s name, purchase amount, sales tax and total amount due.

• Defining diagram

Input Processing Output

Cust_namePurch_amtTax_code

Read customer detailsCompute sales taxCompute total amountPrint customer details

Cust_namePurch_amtSales_taxtotal_amt

Solution AlgorithmProcess_customer_record

1 Read cust_name, purch_amt,tax_code2 IF tax_code = 0 THEN

sales_tax = 0ELSE

IF tax_code = 1 THENsales_tax = purch_amt * 0.03

ELSEIF tax_code = 2 THEN

sales_tax = purch_amt * 0.05ELSE

sales_tax = purch_amt * 0.07ENDIF

ENDIFENDIF

3 total_amt = purch_amt + sales_tax4 Print cust_name, purch_amt, sales_tax, total_amt

END

Desk Checking

Data Set 1 Data Set 2

Purch_amt $ 10.00 $ 20.00

Tax_code 0 2

1. Input Data

2. Expected Results

Data Set 1 Data Set 2

Sales_tax 0 $1.00

Total_amt $10.00 $21.00

3. Desk Check TableStatement

numberPurch_amt Tax_code Sales_tax Total_amt

First Pass

1 $ 10.00 0

2 0

3 $ 10.00

4 print print print

Second Pass

1 $ 20.00 2

2 $ 1.00

3 $ 21.00

4 print print print

Example 4.3 Calculate Employee‘s pay

A program is required by a company to read an employee‘s number, pay rate and the number of hours worked in a week. The program is then to validate the pay rate and the hours worked fields and, if valid, compute the employee‘s weekly pay and print it along with the input data.

Validation: according to the company‘s rules, the maximum hours an employee can work per week is 60 hours, and the maximum hourly rate is $25.00 per hour. If the hours worked field or the hourly rate field is out of range, the input data and appropriate message is to be printed and the employee‘s weekly pay is not to be calculated.

• Weekly pay calculation: Weekly pay is calculated as hours worked times pay rate. If more than 35 hours are worked, payment for the overtime hours worked is calculated at time-and-a-half.

Example 4.3 (cont)

• Defining diagram

Input Processing Output

Emp_noPay_rateHrs_worked

Read employee detailsValidate input fieldsCompute employee payPrint employee details

Emp_noPay_rateHrs_workedEmp_weekly_payError_message

Boolean variables• A variable called as Boolean variable if it contains only one of 2 possible

values (true or false) IF valid_input_fields = true THEN

StatementENDIF

• Can be simplified to imply `= true`: (but must be initially be set to true)IF valid_input_fields THEN

StatementENDIF

• Can also be simplified to imply `= false`:

IF NOT valid_input_fields THENStatement

ENDIF

Solution Algorithm Compute_employee_pay1 Set valid_input_fields to true2 Set error_message to blank3 Read emp_no, pay_rate, hrs_worked4 IF pay_rate > $ 25 THEN

error_message = ´Pay rate exceeds $25.00` Print emp_no, pay_rate, hrs_worked, error_messagevalid_input_fields=false

ENDIF5 IF hrs_worked > 60 THEN

error_message = `Hours worked exceeds 60`Print emp_no, pay_rate, hrs_worked, error_messagevalid_input_fields=false

ENDIF6 IF valid_input_fields THEN

IF hrs_worked <= 35 THENemp_weekly_pay = pay_rate * hrs_worked

ELSEovertime_hrs = hrs_worked – 35overtime_pay = overtime_hrs * pay_rate * 1.5emp_weekly_pay = (pay_rate * 35) + overtime_pay

ENDIFPrint emp_no, pay_rate, hrs_worked, emp_weekly_pay

ENDIFEND

Desk Checking

Data Set 1 Data Set 2

Pay_rate $ 10.00 $ 40.00

Hrs_worked 40 35

1. Input Data

2. Expected Results

Data Set 1 Data Set 2

Pay_rate $ 10.00 $40.00

Hrs_worked 40 35

Emp_weekly_pay

$425.00 -

Error_message blank Pay rate exceeds $25.00

3. Desk Check TableStatement number

Pay_rate Hrs_worked

Over_time_hrs

Over_time_pay

Emp_weekly_pay

Valid_input_fields

Error_message

Print

First Pass

1 true

2 blank

3 $10.00 40

4

5

6 5 75.00 425.00 Print fields

Second Pass

1 true

2 blank

3 $40.00 35

4 false Pay rate exceeds $

25.00

Print message

5

6

The Case Structure

• Keywords: CASE OF and ENDCASE

CASE OF single variablevalue_1 : statement block_1value_2 : statement block_2

.

.

.value_n : statement block_n

ENDCASE

Example 4.4 Process Customer Record

A program is required to read a customer‘s name, a purchase amount and a tax code. The tax code has been validated and will be one of the following:

0 baby needs tax (0%)1 Vegetables and food tax (3%)2 drink sales tax (5%)3 special sales tax (7%)The program must then compute the sales tax and the

total amount due, and print the customer‘s name, purchase amount, sales tax and total amount due.

• Defining diagram

Input Processing Output

Cust_namePurch_amtTax_code

Read customer detailsCompute sales taxCompute total amountPrint customer details

Cust_namePurch_amtSales_taxtotal_amt

Solution Algorithm

Process_customer_record1 Read cust_name, purch_amt,tax_code2 CASE OF tax_code

0 : sales_tax = 01 : sales_tax = purch_amt * 0.032 : sales_tax = purch_amt * 0.053 : sales_tax = purch_amt * 0.07

ENDCASE3 total_amt = purch_amt + sales_tax4 Print cust_name, purch_amt, sales_tax,total_amt

END

Desk Checking

Data Set 1 Data Set 2

Purch_amt $ 10.00 $ 20.00

Tax_code 0 2

1. Input Data

2. Expected Results

Data Set 1 Data Set 2

Sales_tax 0 $1.00

Total_amt $10.00 $21.00

3. Desk Check TableStatement number

Purch_amt Tax_code Sales_tax Total_amt

First Pass

1 $ 10.00 0

2 0

3 $ 10.00

4 print print print

Second Pass

1 $ 20.00 2

2 $ 1.00

3 $ 21.00

4 print print print