Predicate methods (ending with ?) in Ruby - Step-by-Step Execution

Concept Flow - Predicate methods (ending with ?)

Call method ending with ?

↓

Evaluate condition inside method

↓

Return true or false

↓

Use result in if/else or assignment

Predicate methods check a condition and return true or false, helping decisions in code.

Execution Sample

Ruby

def even?(num)
  num % 2 == 0
end

puts even?(4)
puts even?(5)

Defines a predicate method to check if a number is even, then prints true or false.

Execution Table

Step	Action	Input	Condition Evaluated	Return Value	Output
1	Call even?(4)	4	4 % 2 == 0	true	true
2	Print result	true	-	-	true
3	Call even?(5)	5	5 % 2 == 0	false	false
4	Print result	false	-	-	false
5	End	-	-	-	-

💡 All calls completed, program ends.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
num	-	4	5	-
return_value	-	true	false	-

Key Moments - 2 Insights

Why does the method name end with a question mark?

In Ruby, methods ending with ? are predicate methods that return true or false, as shown in steps 1 and 3 of the execution_table.

What does the method return when the condition is false?

The method returns false, as seen in step 3 where even?(5) returns false.

Visual Quiz - 3 Questions

Look at the execution_table, what is the return value when calling even?(4)?

A true

B false

C 4

D nil

💡 Hint

Check step 1 in the execution_table where even?(4) is called.

At which step does the method return false?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look at the return value column in the execution_table.

If we call even?(6), what would be the expected return value?

A false

B true

C 6

D nil

💡 Hint

Refer to the pattern in the execution_table for even numbers returning true.

Concept Snapshot

Predicate methods end with ? and return true or false.
They check a condition inside and return the result.
Used for clear yes/no questions in code.
Example: def even?(num); num % 2 == 0; end
Call with even?(4) returns true.

Full Transcript

Predicate methods in Ruby are special methods that end with a question mark. They always return true or false based on a condition. For example, the method even?(num) checks if a number is even by using the condition num % 2 == 0. When called with 4, it returns true, and with 5, it returns false. These methods help make code easier to read by clearly showing they answer yes/no questions. The execution table shows each step: calling the method, evaluating the condition, returning true or false, and printing the result.