String concatenation and << in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code?

Consider the following Ruby code snippet. What will be printed when it runs?

Ruby

str = "Hello"
str << " World"
puts str

A HelloWorld

B Hello World\n

C Hello World

D Hello << World

💡 Hint

The << operator appends the string on the right to the string on the left with a space if included.

The << operator appends the exact string on the right to the string on the left without adding extra spaces. Since " World" includes a space at the start, the output is "Hello World".

❓ Predict Output

intermediate

What does this code print?

What will be the output of this Ruby code?

Ruby

a = "foo"
b = a
b << "bar"
puts a

A foobar

B foo

C bar

D foobarbar

💡 Hint

Remember that << modifies the original string in place.

Both a and b point to the same string object. Using << on b modifies that object, so a also reflects the change.

🔧 Debug

advanced

Why does this code raise an error?

This Ruby code raises an error. What is the cause?

Ruby

str = nil
str << "test"

A NoMethodError because nil does not have << method

B RuntimeError because string is empty

C TypeError because << expects a number

D SyntaxError due to missing quotes

💡 Hint

Check what methods nil supports.

nil in Ruby does not have the << method, so calling str << "test" when str is nil raises NoMethodError.

🧠 Conceptual

advanced

What is the difference between + and << for strings in Ruby?

Choose the correct statement about the difference between + and << when used with strings in Ruby.

A + and << both modify the original string in place

B + modifies the original string, << creates a new string object

C + and << both create new string objects

D + creates a new string object, << modifies the original string in place

💡 Hint

Think about whether the original string changes after using + or <<.

The + operator returns a new string without changing the original, while << appends to the original string modifying it.

❓ Predict Output

expert

What is the final output of this Ruby code?

Analyze the following Ruby code and determine what it prints.

Ruby

str1 = "abc"
str2 = str1
str1 += "def"
str2 << "xyz"
puts str1
puts str2

A abcdef\nabcdef

B abcdef\nabcxyz

C abcxyz\nabcxyz

D abcdefxyz\nabcdefxyz

💡 Hint

Remember that += creates a new string object, while << modifies the original.

str1 += "def" creates a new string object for str1, so str2 still points to the original "abc". Then str2 << "xyz" modifies that original string. So str1 is "abcdef" and str2 is "abcxyz".