Ruby - Statement for Loops

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Introduction

Ruby's for loop works on a list of items, and it iterates over them, one by one.

For example, here is a for loop that iterates over the items in an array, displaying each in turn: 

for i in [1,2,3] do 
   puts( i ) 
end

The for loop is more like the "for each" iterator.

The items over which the loop iterates don't have to be integers. This works just as well: 

for s in ['one','two','three'] do  
   puts( s ) 
end

Ruby for is "syntax sugar" for the each method, which is implemented by collection types such as Arrays, Sets, Hashes, and Strings.

This is one of the for loops shown earlier rewritten using the each method:

Demo

[1,2,3].each  do |i| 
   puts( i ) 
end

Result

The following examples shows how similar for loops are to each iterators.

Demo

# --- Example 1 --- 
# i) for # from   w w  w.  j ava  2s . c  o  m
for s in ['one','two','three'] do  
   puts( s ) 
end 

# ii) each 
['one','two','three'].each do |s| 
   puts( s ) 
end 

# --- Example 2 --- 
# i) for 
for x in [1, "two", [3,4,5] ] do puts( x ) end   

# ii) each 
[1, "two", [3,4,5] ].each do |x| puts( x ) end

Result

The do keyword is optional in a for loop that spans multiple lines, but it is obligatory when it is written on a single line:

Demo

# Here the 'do' keyword can be omitted 
for s in ['one','two','three']  
   puts( s ) # from   w w  w.j  a va2  s .c  o m
end 

# But here it is required 
for s in ['one','two','three'] do puts( s ) end

Result

This example shows how both for and each can be used to iterate over the values in a range:

Demo

# for 
for s in 1..3 
   puts( s ) #   w  w w  . j ava2  s . com
end 

# each 
(1..3).each do |s| 
   puts(s) 
end

Result

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