Substring in String in Ruby using each_with_index loop

output.txt

1
  Enter a String
  bengaluru
  Enter a Sub String
  uru
  => Present
  
2
  Enter a String
  bengaluru
  Enter a Sub String
  ban
  => NOT Present
  
3
  Enter a String
  bengaluru at 9am
  Enter a Sub String
  at 9
  => Present

4
  Enter a String
  
  Enter a Sub String
  at
  => Not Present
  

substring_in_string.rb

# Substring in String using each_with_index loop

p 'Enter a String'
str = gets.chomp
p 'Enter a Sub String'
sub_str = gets.chomp

def substring_present?(str, sub_str)
    str_ar = str.split('') # convert string to char array
    sub_str_ar = sub_str.split('')

    str_ar.each_with_index do |val, index|
        # if starting char of substring is equal to char in string
        # then check for next substring len of char matches to substring
        if val == sub_str_ar[0] && str[index..index + (sub_str_ar.count - 1)] == sub_str
            return true
        end
    end
    return false
end

if substring_present?(str, sub_str)
    p 'Substring Present'
else
    p 'Substring NOT Present'
end