Substring in String in Ruby using each 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_string1.rb

p 'Enter String'
string = gets.chomp
p 'Enter Sub String'
sub_string = gets.chomp

def sub_string_present?(string, sub_string)
    str_ar = string.split('')
    sub_str_ar = sub_string.split('')

    i = 0
    str_ar.each do |str|
        j = 0
        sub_str_ar.each do |sstr|
            if str_ar[i + j] == sub_str_ar[j]
                if j == (sub_str_ar.count - 1)
                    return true
                end
                j += 1
            else
                break
            end
        end
        i += 1
    end

    return false
end

if sub_string_present?(string, sub_string)
    p 'Present'
else
    p 'Not Present'
end