Interconvert string to int

Given an integer convert it to a string. Given a string convert it into its integer representation.

Solution

String to int

• The trick here is to operate in the ASCII values of the chars
• Parse through the string
  • convert each char into its ascii number,
  • verify it is valid
  • subtract it from the ascii value of 0 to get the numerical value of that char
  • handle the negative case appropriately

    def string_to_int(str)
      i = 0

      if str[0] == '-'
        is_negative = true
        i += 1
      end

      digit = 0
      num = 0

      while i < str.length
        if str[i].ord < '0'.ord || str[i].ord > '9'.ord
          puts 'Invalid input'
          return ''
        end

        digit = str[i].ord - '0'.ord
        num = num * 10 + digit
        i += 1
      end

      is_negative ? -num : num
end

Int to string

• Trick here is to extract one digit at a time from the integer in right to left order starting with the LSB moving towards MSB
• Parse through each digit
  • convert it to char and append to existing chars
  • handle the negative case appropriately

def int_to_string(num)
  return '0' if num == 0

  if num < 0
    is_negative = true
    num = -num
  end

  str = ''

  while num != 0
    digit = num % 10
    num = num / 10
    str = "#{digit}#{str}"
  end

  is_negative ? "-#{str}" : str
end