Check out example codes for "ruby string to int". It will help you in understanding the concepts better.

Code Example 1

Integer('5abc') #=> ArgumentError: invalid value for Integer(): "5abc"
Integer('5') #=> 5

Code Example 2

a = "42" # => '42'
a.to_i # => 42

# But if you might not have a number in your String, you should rather 
# use this instead, as to_i doesn't throw an Error:

"42test123".to_i # => 42
Integer("42test123") # => ArgumentError
Integer("42") # => 42

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