Why does the to_i method result in different o/p's in different situations?

Question

Below is the code which I tried in ruby console. Can anyone tell me why the output is different in this two cases for the same input.

2.1.4 :014 > def a_method
2.1.4 :015?>   puts "enter"
2.1.4 :016?>   a = gets.chomp
2.1.4 :018?>   puts a
2.1.4 :019?>   puts a.to_i
2.1.4 :020?>   end
 => :a_method
2.1.4 :021 > a_method
enter
"12"
"12"
0 (output of a.to_i)
 => nil 

2.1.4 :022 > "12".to_i
 => 12

Here I'm just converting a string number into integer by reading from console using gets, which is giving 0 as output. If I do the same by just giving "12".to_i then I'm getting proper output. Why is that?

Answer 1

This output might help explain the issue:

2.1.1 :001 > def a_method
2.1.1 :002?>   puts "enter"
2.1.1 :003?>   a = gets.chomp
2.1.1 :004?>   puts a.class.name
2.1.1 :005?>   puts a
2.1.1 :006?>   puts a.to_i
2.1.1 :007?>   end
 => :a_method 
2.1.1 :008 > a_method
enter
"12"
String
"12"
0
 => nil 
2.1.1 :009 > a_method
enter
12
String
12
12
 => nil 

gets is short for get string, so if you enter 12 it turns it into "12". As Jiří Pospíšil pointed out, if you enter "12", it turns it into "\"12\"", which to_i is unable to understand.

Answer 2

Inspect the intermediate variable a when entering "12" (with quotes)

a = gets.chomp 
# a => "\"12\""
a.to_i # => 0
"\"12\"".to_i # => 0

If you want to enter the actual number, not a string representation of it, do not use the quotes.