Ruby for Loop

Iterate over ranges and collections

📊 What is a for Loop?

The for loop in Ruby iterates over a range or collection. It's straightforward and familiar to programmers from other languages, though Ruby developers often prefer iterators like each. 


# Basic for loop with range
for i in 1..5
  puts "Number: #{i}"
end

Output: 

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

for Loop Variations

🔢

Range (Inclusive)

Iterate from start to end (includes end) 

for i in 1..3
  puts i
end
# Outputs: 1, 2, 3
📏

Range (Exclusive)

Iterate from start to end (excludes end) 

for i in 1...3
  puts i
end
# Outputs: 1, 2
📦

Array Iteration

Loop through array elements 

for item in [1, 2, 3]
  puts item
end
🔤

String Iteration

Loop through string characters 

for char in "abc".chars
  puts char
end

🔹 for Loop with Ranges

Ranges are the most common way to use for loops. Ruby has two types of ranges: inclusive (..) and exclusive (...). 

# Inclusive range (includes 5)
puts "Inclusive range (1..5):"
for num in 1..5
  puts num
end

# Exclusive range (excludes 5)
puts "\nExclusive range (1...5):"
for num in 1...5
  puts num
end

Output: 

Inclusive range (1..5):
1
2
3
4
5

Exclusive range (1...5):
1
2
3
4

🔹 for Loop with Arrays

You can iterate over arrays using for loops. Each element is accessed one at a time in the order they appear. 

# Loop through array of strings
fruits = ["apple", "banana", "cherry"]
for fruit in fruits
  puts "I like #{fruit}s"
end

# Loop through array of numbers
numbers = [10, 20, 30, 40]
sum = 0
for num in numbers
  sum += num
end
puts "Total sum: #{sum}"

Output: 

I like apples
I like bananas
I like cherrys
Total sum: 100

🔹 Nested for Loops

You can nest for loops inside each other to work with multi-dimensional data or create patterns like multiplication tables. 

# Simple multiplication table
for i in 1..3
  for j in 1..3
    print "#{i}x#{j}=#{i*j} "
  end
  puts  # New line after each row
end

# Pattern printing
for row in 1..4
  for col in 1..row
    print "* "
  end
  puts
end

Output: 

1x1=1 1x2=2 1x3=3 
2x1=2 2x2=4 2x3=6 
3x1=3 3x2=6 3x3=9 
* 
* * 
* * * 
* * * *

🔹 for Loop with Strings

To iterate over characters in a string, you need to convert it to an array of characters using the .chars method: 

# Iterate through string characters
word = "Ruby"
for letter in word.chars
  puts "Letter: #{letter}"
end

# Count vowels in a string
text = "Hello World"
vowel_count = 0
for char in text.downcase.chars
  if ['a', 'e', 'i', 'o', 'u'].include?(char)
    vowel_count += 1
  end
end
puts "Vowels found: #{vowel_count}"

Output: 

Letter: R
Letter: u
Letter: b
Letter: y
Vowels found: 3

🔹 for Loop vs each Method

In Ruby, the each method is generally preferred over for loops. Here's a comparison to help you understand both approaches: 

# Using for loop
puts "Using for loop:"
for i in 1..3
  puts i
end

# Using each method (more Ruby-like)
puts "\nUsing each method:"
(1..3).each do |i|
  puts i
end

# Both produce the same output!
# But 'each' is more idiomatic in Ruby

Output: 

Using for loop:
1
2
3

Using each method:
1
2
3

Why Ruby developers prefer 'each':

  • Scope: Variables in 'each' blocks are local to the block
  • Functional style: 'each' fits Ruby's functional programming style better
  • Chainable: You can chain other methods after 'each'
  • Convention: It's the Ruby way and what most Rubyists expect

🔹 Practical for Loop Examples

Here are some real-world examples where for loops can be useful: 

# Calculate factorial
n = 5
factorial = 1
for i in 1..n
  factorial *= i
end
puts "Factorial of #{n} is #{factorial}"

# Generate a list of squares
squares = []
for num in 1..5
  squares << num ** 2
end
puts "Squares: #{squares.join(', ')}"

# Process temperature readings
temperatures = [72, 75, 68, 80, 77]
for temp in temperatures
  if temp > 75
    puts "#{temp}°F - Hot!"
  else
    puts "#{temp}°F - Comfortable"
  end
end

Output: 

Factorial of 5 is 120
Squares: 1, 4, 9, 16, 25
72°F - Comfortable
75°F - Comfortable
68°F - Comfortable
80°F - Hot!
77°F - Hot!

🧠 Test Your Knowledge

What's the difference between 1..5 and 1...5 in a for loop?