cheat sheets.

"1".to_i         # => 1
Integer("1")     # => 1

"2two".to_i      # => 2
Integer("2two")  # => ArgumentError: invalid value for Integer: "2two"

"three".to_i     # => 0
Integer("three") # => ArgumentError: invalid value for Integer: "three"

"100".to_i(16) # => 256
"foo".to_i(36) # => 20328

Time.now.to_i # => 1227934942
open('foo.txt').to_i # => 3

nil.to_i # => 0