Loops and Iterators in ruby

The loops execute the same code again and again. Assume you want to print your name 100 times then you need not to write print statement 100 times. Here you can use loop for executing same code 100 times.

while statement:

In while loop, we define a condition. Until condition is fulfilling, the code inside the loop will execute again and again.

# initialize a variable
a = 0

# while statement with condition
while a < 3
  # code inside while loop
  puts 'harish'
  # modifiing condition
  a+=1
  # finish loop with end
end

Output:

harish
harish
harish

In this example, we are defining a variable 'a' and putting a condition on it. Until 'a' is less then 3, while loop will print 'harish'.

while modifier:

There are two types of modified statements. First is one line while statement. The syntax is => expression while condition.

# initialize a variable
a = 0

# modified while statement with condition
a = gets.to_i while a < 3

This program will take input from user until user do not enter a number larger than or equal to 3.

Syntax of second type statement is:

begin
    # code
end while condition

If you are coming from C, C++ or java programming language then this type of statement is 'do while statement' in these languages. The code inside the begin block will execute once before checking the condition. In other words, this statement execute code first and checks condition after it for next iteration.

# initialize a variable
a = 0

# modified while statement with condition
begin
  puts a
  a+=1
end while a <3

until statement:

Until statement similar to while loop but only difference is that it executes when condition is false.

# initialize a variable
a = 0

# until statement with condition
until a > 3
  # code inside until loop
  puts 'harish'
  # modifiing condition
  a+=1
  # finish loop with end
end

Above until statement will execute until 'a' is not grater then 3.

Output:

harish
harish
harish
harish

until modifier:

It is same as while modifier but code executes when condition is false.

# initialize a variable
a = 0

# modified until statement with condition
a = gets.to_i until a > 3

Until 'a' is not greater then 3, this code will take a value for 'a'.

Example of second type is:

# initialize a variable
a = 0

# modified until statement with condition
begin
  puts a
  a+=1
end until a > 3

Output:

0
1
2
3

for statement:

# initialize an array
array = [12,32,3,132,123,34]

# define for loop statement
# local is a local variable, accessible only in for loop
for local in array
  # code inside for loop
  puts local
  # end for loop
end

Output:

12
32
3
132
123
34

This statement takes an array and define a local variable. This variable is assigned next value of the array every iteration starting from first.

break, next and redo statements:

These statements are used to disturb the regular execution of the loops and iterators.

1. break : It is used to stop the execution of the loop.
2. next : It is used to skip current executing iterator only. It is same as 'continue' in C, C++ and Java.
3. redo: When this statement executes the loop again starts execution from starting.

# initialize an array
array = [12,32,3,132,123,34]

a = 0
puts 'use of break statement:'
# use of break statement
while a < 10 
  a+=1
  puts a
  if a == 5
    # skip loop if a = 5
    break
  end
end

a = 0
puts 'use of next statement:'
while a < 10
  a+=1
  # don't print 5
  if a == 5
    next
  end
  puts a
end
a = 0
puts 'use of redo'
# first time value of a is 0
while a < 5
  a+=1
  
  # if a = 3 then repeat the loop
  # value of a will not change i.e. second time value will be 3 not 0
  if a == 3
    redo
  end
  puts a
end

Output:

use of break statement:
1
2
3
4
5
use of next statement:
1
2
3
4
6
7
8
9
10
use of redo
1
2
4
5

each and collect iterators

Each iterator is same as for loop.

array = [12,23,34,45,56,67,7]

# each iterator also defines a local variable
array.each do |local|
  # print each value of array one by one
  puts local
end

Collect iterator return iterators with same elements.

array = [12,23,34,45,56,67,7]

b = array.collect
for i in b
  puts i
end

Output:

12
23
34
45
56
67
7