String interpolation with #{} in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is string interpolation in Ruby?

String interpolation in Ruby is a way to insert the value of a variable or expression directly into a string using #{ } inside double quotes.

beginner

How do you write a string with a variable inside it using interpolation?

Use double quotes and place the variable inside #{ }. For example: "Hello, #{name}!" will insert the value of the variable name.

intermediate

Why does string interpolation only work with double quotes and not single quotes?

Ruby treats single-quoted strings as plain text and does not process #{ } inside them. Double-quoted strings allow Ruby to evaluate the code inside #{ }.

beginner

Example: What is the output of this Ruby code? name = "Sam"; puts "Hi, #{name}!"

The output will be: Hi, Sam! The #{name} is replaced by the value of the variable name.

intermediate

Can you put any Ruby expression inside #{ } in a string?

Yes! You can put any Ruby code that returns a value inside #{ }, like calculations or method calls, and Ruby will insert the result into the string.

Which of these strings will correctly show the value of variable age using interpolation?

A "I am #{age} years old."

B 'I am #{age} years old.'

C "I am $age years old."

D 'I am $age years old.'

Only double-quoted strings with #{ } will evaluate the variable age. Single quotes treat it as plain text.

What will this code print? puts "2 + 3 = #{2 + 3}"

A 2 + 3 = #{2 + 3}

B 2 + 3 = 2 + 3

C 2 + 3 = 5

D Error

The expression inside #{ } is evaluated, so 2 + 3 becomes 5.

What happens if you use single quotes with #{ } like '#{name}'?

A It removes the #{ }

B It shows the value of name

C It causes an error

D It shows the text #{name} literally

Single quotes do not evaluate #{ }, so it prints the text as is.

Which is true about string interpolation in Ruby?

A It works only with numbers

B It only works inside double-quoted strings

C It only works inside single-quoted strings

D It works inside both single and double quotes

Ruby evaluates #{ } only inside double-quoted strings.

Can you put method calls inside #{ } in a string?

A Yes, Ruby evaluates any expression inside #{ }

B No, only variables are allowed

C Only numbers are allowed

D Only strings are allowed

Any Ruby expression, including method calls, can be inside #{ } and will be evaluated.

Explain how string interpolation works in Ruby and why double quotes are necessary.

Think about how Ruby treats single vs double quotes.

Give an example of using string interpolation with a variable and with a calculation inside the string.

Try to show both simple and expression interpolation.