Variables and data storage in Intro to Computing - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ trace

intermediate

Trace the value of variable after assignments

Consider the following steps where a variable is assigned new values. What is the final value of x after all steps?

Intro to Computing

x = 5
x = x + 3
x = x * 2
x = x - 4

A 12

B 16

C 10

D 8

💡 Hint

Calculate step by step: start with 5, add 3, then multiply by 2, then subtract 4.

Start with x = 5. Then x + 3 = 8. Next multiply by 2: 8 * 2 = 16. Finally subtract 4: 16 - 4 = 12. So the final value is 12.

🧠 Conceptual

intermediate

Identify the correct description of variable storage

Which option best describes what happens when a variable stores a value in a computer?

A The variable changes the value into a picture.

B The variable sends the value to the screen immediately.

C The variable deletes the value after storing it.

D The variable creates a box in memory that holds the value.

💡 Hint

Think about how a variable keeps information for later use.

A variable acts like a labeled box in the computer's memory where a value is kept until needed. It does not send the value to the screen or delete it immediately.

❓ Comparison

advanced

Compare variable types and their storage sizes

Which option correctly orders these variable types from smallest to largest typical storage size?

A Integer, Boolean, String, Floating-point

B String, Boolean, Integer, Floating-point

C Boolean, Integer, Floating-point, String

D Floating-point, Integer, Boolean, String

💡 Hint

Think about how much space each type usually needs in memory.

Booleans usually need 1 bit or byte, integers need more bytes, floating-point numbers need even more, and strings can vary but often require the most space.

❓ identification

advanced

Identify the error in variable naming

Which variable name is invalid in most programming languages?

A user_name

B 2ndPlace

C _tempValue

D totalScore

💡 Hint

Variable names usually cannot start with a number.

Variable names cannot start with digits. Option B starts with '2', which is invalid. Other options start with letters or underscore, which are allowed.

🚀 Application

expert

Determine the output after variable swapping

Given the code below, what is the value of a and b after execution?

Intro to Computing

a = 10
b = 20
a, b = b, a

A a = 20, b = 10

B a = 10, b = 20

C a = 30, b = 0

D a = 20, b = 20

💡 Hint

Look at how the values are swapped in one line.

The line a, b = b, a swaps the values of a and b. So a becomes 20 and b becomes 10.

Practice

1. What is a variable in computing?
Example: Think of a variable as a labeled box where you can store something.

easy

A. A container that holds data values

B. A type of computer hardware

C. A program that runs automatically

D. A tool to clean computer screens

Solution

1. Step 1: Understand the concept of variables

   A variable is like a labeled box where you can store data such as numbers or words.

2. Step 2: Match the description to the options

   A container that holds data values describes a container holding data values, which matches the idea of a variable.

3. Final Answer:

   A container that holds data values -> Option A

4. Quick Check:

   Variable = labeled box for data [OK]

Hint: Variables store data like boxes hold items [OK]

Common Mistakes:

• Confusing variables with hardware
• Thinking variables run programs
• Mixing variables with tools or devices

2. Which of the following is the correct way to create a variable named age and store the number 25 in it?

easy

A. int age = 25

B. age = 25

C. age := 25

D. 25 = age

Solution

1. Step 1: Identify the correct assignment syntax

   In many programming languages, assigning a value to a variable uses the format: variable = value.

2. Step 2: Check each option

   age = 25 uses age = 25, which is the standard way to assign 25 to variable age.

3. Final Answer:

   age = 25 -> Option B

4. Quick Check:

   Variable assignment uses = sign [OK]

Hint: Variable name on left, value on right with = [OK]

Common Mistakes:

• Putting value before variable
• Using wrong assignment symbols
• Confusing variable declaration syntax

3. What will be the value of total after running this code?

price = 10
quantity = 3
total = price * quantity

medium

A. 30

B. 13

C. 103

D. Error

Solution

1. Step 1: Understand the variables and operation

   price is 10, quantity is 3, and total is assigned price multiplied by quantity.

2. Step 2: Calculate the multiplication

   10 * 3 = 30, so total will be 30.

3. Final Answer:

   30 -> Option A

4. Quick Check:

   10 x 3 = 30 [OK]

Hint: Multiply values stored in variables [OK]

Common Mistakes:

• Adding instead of multiplying
• Concatenating numbers as strings
• Expecting syntax error

4. Identify the error in this code snippet:

number = 5
Number = 10
print(number + Number)

medium

A. Missing semicolon at the end of lines

B. Cannot add two variables together

C. Variables must start with a capital letter

D. Variable names are case-sensitive, so both are different variables

Solution

1. Step 1: Check variable names and case sensitivity

   Variables number and Number differ by case and are treated as two separate variables.

2. Step 2: Understand the addition operation

   Adding number (5) and Number (10) is valid and results in 15.

3. Final Answer:

   Variable names are case-sensitive, so both are different variables -> Option D

4. Quick Check:

   Case matters in variable names [OK]

Hint: Remember variable names are case-sensitive [OK]

Common Mistakes:

• Assuming variables with different cases are same
• Expecting syntax error for missing semicolons
• Thinking variables can't be added

5. You want to store the names and ages of three friends in variables. Which approach correctly uses variables to store this data for easy access later?

hard

A. name1 = 'Anna'; age1 = 20; name2 = 'Ben'; age2 = 22; name3 = 'Cara'; age3 = 19

B. friends = ['Anna', 20, 'Ben', 22, 'Cara', 19]

C. friends = {'Anna': 20, 'Ben': 22, 'Cara': 19}

D. names = ['Anna', 'Ben', 'Cara']; ages = [20, 22, 19]

Solution

1. Step 1: Understand the need for easy access to names and ages

   We want to link each friend's name to their age clearly and accessibly.

2. Step 2: Evaluate each option's data structure

   friends = {'Anna': 20, 'Ben': 22, 'Cara': 19} uses a dictionary (key-value pairs) where names are keys and ages are values, making access easy and clear.

3. Final Answer:

   friends = {'Anna': 20, 'Ben': 22, 'Cara': 19} -> Option C

4. Quick Check:

   Use key-value pairs for related data [OK]

Hint: Use key-value pairs to link related data [OK]

Common Mistakes:

• Using separate variables for each item
• Mixing names and ages in one list without structure
• Using parallel lists which are harder to manage