Dynamic typing vs strong typing in Ruby - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code with dynamic typing?

Consider this Ruby code snippet. What will it print?

Ruby

x = 10
x = "hello"
puts x

A nil

B 10

C hello

D TypeError

💡 Hint

In Ruby, variables can hold any type and can change type.

Ruby is dynamically typed, so the variable x can hold an integer first, then a string. The last value assigned is printed.

❓ Predict Output

intermediate

What error does this Ruby code raise due to strong typing?

What error will this Ruby code produce?

Ruby

a = 5
b = "3"
puts a + b

A 8

B TypeError

C ArgumentError

D NoMethodError

💡 Hint

Ruby does not automatically convert between strings and numbers for addition.

Ruby is strongly typed, so adding an integer and a string without conversion causes a TypeError.

🧠 Conceptual

advanced

Which statement best describes Ruby's typing system?

Choose the statement that correctly describes Ruby's typing.

A Ruby is dynamically typed and strongly typed.

B Ruby is statically typed and weakly typed.

C Ruby is statically typed and strongly typed.

D Ruby is dynamically typed and weakly typed.

💡 Hint

Think about when types are checked and if implicit conversions happen.

Ruby checks types at runtime (dynamic typing) and does not allow implicit type coercion in operations (strong typing).

❓ Predict Output

advanced

What is the output of this Ruby code mixing types?

What will this Ruby code print?

Ruby

def add(x, y)
  x + y
end

puts add(2, 3)
puts add("2", "3")
puts add(2, "3")

A

5
23
TypeError

B

5
23
5

C

TypeError
TypeError
TypeError

D

5
TypeError
TypeError

💡 Hint

Consider how Ruby handles addition for integers and strings, and what happens when types differ.

Adding integers works (5). Adding strings concatenates ("23"). Adding integer and string causes TypeError.

🧠 Conceptual

expert

Why does Ruby raise a TypeError when adding integer and string?

Choose the best explanation for why Ruby raises a TypeError when adding an integer and a string.

A Because Ruby is dynamically typed and allows any operation between types.

B Because Ruby automatically converts strings to integers but fails here due to syntax.

C Because Ruby is statically typed and checks types at compile time.

D Because Ruby is strongly typed and does not perform implicit type conversion between incompatible types.

💡 Hint

Think about how Ruby treats types during operations and if it converts types automatically.

Ruby's strong typing means it forbids operations between incompatible types without explicit conversion, causing TypeError.

Practice

1. Which statement best describes Ruby's typing system?

easy

A. Ruby is dynamically typed and strongly typed.

B. Ruby is statically typed and weakly typed.

C. Ruby is statically typed and strongly typed.

D. Ruby is dynamically typed and weakly typed.

Solution

1. Step 1: Understand dynamic typing

   Dynamic typing means variables can hold any type and change types anytime during execution.

2. Step 2: Understand strong typing

   Strong typing means the language prevents mixing incompatible types without explicit conversion.

3. Final Answer:

   Ruby is dynamically typed and strongly typed. -> Option A

4. Quick Check:

   Dynamic + Strong = C [OK]

Hint: Remember Ruby allows type changes but checks type safety [OK]

Common Mistakes:

• Confusing dynamic with static typing
• Thinking Ruby allows unsafe type mixing
• Mixing weak and strong typing concepts

2. Which Ruby code snippet shows dynamic typing in action?

easy

A. x = 10; x = "hello"

B. int x = 10; x = "hello"

C. var x: Integer = 10; x = "hello"

D. let x = 10; x = true

Solution

1. Step 1: Identify Ruby syntax

   Ruby allows assigning different types to the same variable without error.

2. Step 2: Check each option

   x = 10; x = "hello" uses Ruby syntax and changes x from integer to string, showing dynamic typing.

3. Final Answer:

   x = 10; x = "hello" -> Option A

4. Quick Check:

   Variable changes type dynamically = A [OK]

Hint: Look for variable reassignment with different types in Ruby syntax [OK]

Common Mistakes:

• Choosing code with static typing syntax
• Confusing variable declaration styles
• Ignoring language-specific syntax rules

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

def add(a, b)
  a + b
end

puts add(5, "10")

medium

A. 15

B. TypeError

C. 510

D. nil

Solution

1. Step 1: Analyze the method call

   The method add tries to add an integer (5) and a string ("10") using + operator.

2. Step 2: Understand Ruby's strong typing

   Ruby does not automatically convert types for +; adding integer and string causes a TypeError.

3. Final Answer:

   TypeError -> Option B

4. Quick Check:

   Strong typing prevents int + string = B [OK]

Hint: Adding different types without conversion causes TypeError [OK]

Common Mistakes:

• Assuming automatic string conversion
• Expecting concatenation of numbers and strings
• Ignoring Ruby's type safety rules

4. Identify the error in this Ruby code:

def multiply(x, y)
  x * y
end

result = multiply(3, "4")
puts result

medium

A. NameError for undefined variable

B. SyntaxError due to method definition

C. No error, outputs 12

D. TypeError due to multiplying integer and string

Solution

1. Step 1: Check method parameters and call

   The method multiply is called with an integer (3) and a string ("4").

2. Step 2: Understand Ruby's type rules for *

   Multiplying integer by string without conversion causes a TypeError in Ruby.

3. Final Answer:

   TypeError due to multiplying integer and string -> Option D

4. Quick Check:

   Strong typing blocks int * string = A [OK]

Hint: Check operand types for * operator to avoid TypeError [OK]

Common Mistakes:

• Thinking Ruby auto-converts string to integer
• Assuming no error on mixed types
• Confusing SyntaxError with TypeError

5. You want to write a Ruby method that adds two values but safely handles if one is a string representing a number. Which approach best uses Ruby's dynamic and strong typing?

hard

A. Convert both to strings and concatenate.

B. Add values directly without conversion.

C. Convert both to integers before adding using to_i method.

D. Use static type declarations for parameters.

Solution

1. Step 1: Understand dynamic typing flexibility

   Ruby variables can hold any type, so inputs can be string or integer.

2. Step 2: Use strong typing safety

   To avoid TypeError, convert strings to integers explicitly before adding.

3. Step 3: Evaluate options

   Converting both to integers using to_i before adding is safe. Adding directly risks TypeError. Static type declarations are invalid in Ruby. Converting to strings performs concatenation instead of addition.

4. Final Answer:

   Convert both to integers before adding using to_i method. -> Option C

5. Quick Check:

   Dynamic + Strong typing = explicit conversion [OK]

Hint: Convert strings to numbers before math to avoid errors [OK]

Common Mistakes:

• Ignoring type conversion before arithmetic
• Assuming Ruby auto-converts types
• Using static typing syntax in Ruby