"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 # => 0cheat sheets.
$ cheat to_i