Meaningful identifiers for variables and constants

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. Which identifier is better for a variable that stores the total cost of a customer's shopping?

A TotalToPay

B T

2. Which identifier is better for a variable that stores how much an employee earns per hour?

A HourlyRate

B X

3. Why should a programmer choose meaningful identifiers?

A They make the program run faster

B They make the program easier to read and maintain

4. Which line is easier to understand?

A T ← P * Q

B TotalToPay ← Price * Quantity

5. When is a single-letter identifier acceptable?

A As an index in a loop, such as i or j

B For a value such as a customer's total bill

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1DECLARE TotalToPay : REAL		AA meaningful identifier: the name tells the reader the variable holds the total amount a customer has to pay
2CONSTANT HourlyRate ← 12.50		BT is a poor identifier because it does not say what it holds. Rename it to something like TotalToPay so the purpose is clear.
3A single letter name is acceptable when it is conventional, such as i as an index counting through an array		CX ← X + 1
4Single letters are also conventional for coordinates, such as X and Y for a position on a grid		DA meaningful constant name that says the fixed value is the pay for each hour worked
5T ← Price * Quantity		EFOR i ← 1 TO 10
6X ← Hours * Rate		FX is used for a pay amount, but X normally means a coordinate. Rename it to something like TotalPay to show what it holds.

Definitions

meaningful identifier

Fill in the Blanks

Complete each line of code by filling in the missing parts.

CONSTANT VatRate ← 0.2 Price ← 50 TotalToPay ← Price + Price * _______

HourlyRate ← 15 HoursWorked ← 40 __________ ← HourlyRate * HoursWorked

X ← 4 // horizontal position _ ← 7 // vertical position OUTPUT X, Y

Hours ← 8 __________ ← 12.5 Pay ← Hours * HourlyRate

CONSTANT PassMark ← 50 INPUT Mark IF Mark >= ________ THEN

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A DECLARE HourlyRate : REAL

B DECLARE TotalToPay : REAL

C HourlyRate ← 12.5

D X ← HourlyRate * 8

Question 2

A X ← 12.5

B Hours ← 8

C Wage ← HourlyRate * Hours

D OUTPUT Wage

Question 3

A T ← 0

B TotalToPay ← TotalToPay + 4.5

C OUTPUT TotalToPay

Question 4

A DECLARE Name : STRING

B INPUT Name

C X ← LENGTH(Name)

D OUTPUT NameLength

Question 5

A CONSTANT VatRate ← 0.2

B INPUT Price

C A ← Price * VatRate

D OUTPUT VatAmount

Answer Key

Meaningful identifiers for variables and constants

Section A: Quick Questions

A — TotalToPay

A — HourlyRate

B — They make the program easier to read and maintain

B — TotalToPay ← Price * Quantity

A — As an index in a loop, such as i or j

Section B: Match the Pairs

DECLARE TotalToPay : REAL → A meaningful identifier: the name tells the reader the variable holds the total amount a customer has to pay

CONSTANT HourlyRate ← 12.50 → A meaningful constant name that says the fixed value is the pay for each hour worked

A single letter name is acceptable when it is conventional, such as i as an index counting through an array → FOR i ← 1 TO 10

Single letters are also conventional for coordinates, such as X and Y for a position on a grid → X ← X + 1

T ← Price * Quantity → T is a poor identifier because it does not say what it holds. Rename it to something like TotalToPay so the purpose is clear.

X ← Hours * Rate → X is used for a pay amount, but X normally means a coordinate. Rename it to something like TotalPay to show what it holds.

Section C: Definitions

meaningful identifier — A name that describes what a variable or constant holds, such as TotalToPay instead of T, so the program is easy to read and maintain.

Section D: Fill in the Blanks

CONSTANT VatRate ← 0.2
Price ← 50
TotalToPay ← Price + Price * VatRate

HourlyRate ← 15
HoursWorked ← 40
TotalToPay ← HourlyRate * HoursWorked

X ← 4 // horizontal position
Y ← 7 // vertical position
OUTPUT X, Y

Hours ← 8
HourlyRate ← 12.5
Pay ← Hours * HourlyRate

CONSTANT PassMark ← 50
INPUT Mark
IF Mark >= PassMark THEN

Section E: Spot the Error

D — X says nothing about what it holds. The variable declared to hold the final amount is TotalToPay, so the line should be TotalToPay ← HourlyRate * 8.

A — A single letter X does not tell the reader this is the pay per hour. It should be HourlyRate ← 12.5, which also matches its use on line 3.

A — T is a poor name because it does not describe the value. The variable should be TotalToPay so that every line of the program refers to the same meaningful identifier.

C — X does not describe the number of characters it stores. A meaningful name such as NameLength should be used: NameLength ← LENGTH(Name).

C — The single letter A hides that this value is the VAT charged. It should be VatAmount ← Price * VatRate so the program is easy to read.