Local variables and naming conventions in Ruby - Mini Project: Build & Apply

Local variables and naming conventions

📖 Scenario: You are helping a small bakery keep track of daily sales. You will use local variables with clear names to store and calculate the total number of bread loaves sold.

🎯 Goal: Create local variables with proper names to store daily sales numbers, add them up, and print the total loaves sold.

📋 What You'll Learn

Create local variables with lowercase letters and underscores

Use descriptive variable names for daily sales

Add the daily sales variables to get the total

Print the total number of loaves sold

💡 Why This Matters

🌍 Real World

Local variables are used everywhere in programming to store temporary information like daily sales, user input, or calculation results.

💼 Career

Clear variable naming and using local variables properly is a fundamental skill for any programmer, making your code easier to maintain and collaborate on.

1

Create local variables for daily sales

Create three local variables called monday_sales, tuesday_sales, and wednesday_sales with the values 20, 25, and 30 respectively.

Ruby

# Create local variables monday_sales, tuesday_sales, wednesday_sales with values 20, 25, 30
# Your code here

Hint

Use lowercase letters and underscores for variable names. Assign the exact numbers given.

2

Create a variable for total sales

Create a local variable called total_sales and set it to the sum of monday_sales, tuesday_sales, and wednesday_sales.

Ruby

monday_sales = 20
tuesday_sales = 25
wednesday_sales = 30
# Create total_sales as the sum of monday_sales, tuesday_sales, and wednesday_sales
# Your code here

Hint

Add the three daily sales variables and store the result in total_sales.

3

Print the total sales

Use puts to print the value of total_sales.

Ruby

monday_sales = 20
tuesday_sales = 25
wednesday_sales = 30
total_sales = monday_sales + tuesday_sales + wednesday_sales
# Print total_sales
# Your code here

Hint

Use puts followed by the variable name to display the total.

4

Run the program and see the output

Run the program to display the total number of bread loaves sold over the three days.

Ruby

monday_sales = 20
tuesday_sales = 25
wednesday_sales = 30
total_sales = monday_sales + tuesday_sales + wednesday_sales
puts total_sales
# Run the program

Hint

The output should be the sum of 20, 25, and 30, which is 75.

Practice

1. Which of the following is a valid local variable name in Ruby?

easy

A. user_name

B. UserName

C. user-name

D. 1username

Solution

1. Step 1: Check the first character of each variable name

   Local variables must start with a lowercase letter or underscore. 'user_name' starts with 'u' which is lowercase.

2. Step 2: Check for invalid characters

   Variable names cannot contain hyphens or start with numbers. 'user-name' has a hyphen and '1username' starts with a number, so they are invalid.

3. Final Answer:

   user_name -> Option A

4. Quick Check:

   Valid local variable = user_name [OK]

Hint: Local variables start lowercase or underscore, no hyphens or digits first [OK]

Common Mistakes:

• Starting variable names with uppercase letters
• Using hyphens instead of underscores
• Starting variable names with numbers

2. Which of these Ruby variable names will cause a syntax error?

easy

A. temp-var

B. tempVar2

C. _tempVar

D. temp_var

Solution

1. Step 1: Identify invalid characters in variable names

   Ruby variable names can only contain letters, digits, and underscores. Hyphens are not allowed.

2. Step 2: Check each option for invalid characters

   temp-var has a hyphen, which causes a syntax error. The others are valid.

3. Final Answer:

   temp-var -> Option A

4. Quick Check:

   Hyphens cause syntax errors in variable names [OK]

Hint: No hyphens allowed in variable names, use underscores instead [OK]

Common Mistakes:

• Using hyphens instead of underscores
• Confusing uppercase and lowercase letters
• Starting variable names with digits

3. What will be the output of this Ruby code?

def greet
  name = "Alice"
  Name = "Bob"
  puts name
end
greet

medium

A. name

B. Alice

C. Bob

D. Name

Solution

1. Step 1: Understand variable naming and scope

   In Ruby, local variables start with lowercase letters, constants start with uppercase. 'name' is local variable, 'Name' is a constant.

2. Step 2: Check which variable is printed

   The code prints 'name', which is "Alice". The constant 'Name' is not used in the puts statement.

3. Final Answer:

   Alice -> Option B

4. Quick Check:

   Local variable 'name' prints "Alice" [OK]

Hint: Local variables lowercase, constants uppercase; puts prints local variable [OK]

Common Mistakes:

• Confusing constants with local variables
• Assuming uppercase variable prints
• Ignoring case sensitivity

4. Identify the error in this Ruby code snippet:

def calculate
  total = 10
  Total = 20
  puts Total + total
end
calculate

medium

A. SyntaxError due to variable naming

B. Runtime error: undefined variable

C. No error, outputs 30

D. No error, outputs 10

Solution

1. Step 1: Analyze variable types and naming

   'total' is a local variable, 'Total' is a constant. Both are defined before use.

2. Step 2: Evaluate the expression in puts

   Adding 'Total' (20) and 'total' (10) results in 30. No syntax or runtime errors occur.

3. Final Answer:

   No error, outputs 30 -> Option C

4. Quick Check:

   Constant + local variable sums correctly [OK]

Hint: Constants uppercase, locals lowercase; both can be used together [OK]

Common Mistakes:

• Assuming case-insensitive variables
• Expecting syntax error from uppercase variable
• Confusing constants with local variables

5. You want to create a local variable to store a user's age in Ruby. Which of these variable names follows best naming conventions and is clear to other programmers?

hard

A. UserAge

B. userAge

C. user-age

D. user_age

Solution

1. Step 1: Check Ruby naming conventions for local variables

   Local variables should start with lowercase letters or underscores and use underscores to separate words for clarity.

2. Step 2: Evaluate each option for clarity and convention

   'user_age' uses lowercase and underscores, making it clear and conventional. 'UserAge' starts uppercase (looks like constant), 'user-age' has invalid hyphen, 'userAge' uses camelCase which is less common in Ruby.

3. Final Answer:

   user_age -> Option D

4. Quick Check:

   Use lowercase with underscores for clear local variables [OK]

Hint: Use lowercase and underscores for clear Ruby local variables [OK]

Common Mistakes:

• Using camelCase instead of snake_case
• Starting variable names with uppercase letters
• Using hyphens in variable names