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sabomi's solution

to Binary in the PL/SQL Track

Published at Jul 13 2018 · 1 comment
Instructions
Test suite
Solution

Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.

Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.

Note

  • Implement the conversion yourself. Do not use something else to perform the conversion for you.

About Binary (Base-2)

Decimal is a base-10 system.

A number 23 in base 10 notation can be understood as a linear combination of powers of 10:

  • The rightmost digit gets multiplied by 10^0 = 1
  • The next number gets multiplied by 10^1 = 10
  • ...
  • The nth number gets multiplied by 10^(n-1).
  • All these values are summed.

So: 23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10

Binary is similar, but uses powers of 2 rather than powers of 10.

So: 101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10.

Setup

Go through the setup instructions for PL/SQL to get ready to code:

http://exercism.io/languages/plsql

Running the Tests

Execute the tests by calling the run method in the respective ut_<exercise># package. The necessary code should be contained at the end of the test package. As an example, the test for the hamming exercise would be run using

begin
  ut_hamming#.run;
end;
/

Source

All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

ut_binary#.plsql

create or replace package ut_binary#
is
  procedure run;
end ut_binary#;
/
 
create or replace package body ut_binary#
is
  procedure test (
    i_descn                                       varchar2
   ,i_exp                                         pls_integer
   ,i_act                                         pls_integer
  )
  is
  begin
    if i_exp = i_act then
      dbms_output.put_line('SUCCESS: ' || i_descn);
    else
      dbms_output.put_line('FAILURE: ' || i_descn || ' - expected ' || nvl('' || i_exp, 'null') || ', but received ' || nvl('' || i_act, 'null'));
    end if;
  end test;
 
  procedure run
  is
  begin
    test(i_descn => 'test_binary_1_is_decimal_1'              , i_exp => 1   , i_act => binary#.to_decimal('1'          ));
    test(i_descn => 'test_binary_10_is_decimal_2'             , i_exp => 2   , i_act => binary#.to_decimal('10'         ));
    test(i_descn => 'test_binary_11_is_decimal_3'             , i_exp => 3   , i_act => binary#.to_decimal('11'         ));
    test(i_descn => 'test_binary_100_is_decimal_4'            , i_exp => 4   , i_act => binary#.to_decimal('100'        ));
    test(i_descn => 'test_binary_1001_is_decimal_9'           , i_exp => 9   , i_act => binary#.to_decimal('1001'       ));
    test(i_descn => 'test_binary_11010_is_decimal_26'         , i_exp => 26  , i_act => binary#.to_decimal('11010'      ));
    test(i_descn => 'test_binary_10001101000_is_decimal_1128' , i_exp => 1128, i_act => binary#.to_decimal('10001101000'));
    test(i_descn => 'test_invalid_binary_postfix_is_decimal_0', i_exp => 0   , i_act => binary#.to_decimal('10110a'     ));
    test(i_descn => 'test_invalid_binary_prefix_is_decimal_0' , i_exp => 0   , i_act => binary#.to_decimal('a10110'     ));
    test(i_descn => 'test_invalid_binary_infix_is_decimal_0'  , i_exp => 0   , i_act => binary#.to_decimal('101a10'     ));
    test(i_descn => 'test_invalid_binary_is_decimal_0'        , i_exp => 0   , i_act => binary#.to_decimal('101210'     ));
  end run;
end ut_binary#;
/
 
begin
  ut_binary#.run;
end;
/
create or replace package binary#
is
  --+--------------------------------------------------------------------------+
  -- Convert a binary number, represented as a string (e.g. '101010'), 
  -- to its decimal equivalent 
  --+--------------------------------------------------------------------------+

  function to_decimal (
    binary_string                             varchar2
  ) return pls_integer;
  
   
end binary#;
/

create or replace package body binary#
is
   function to_decimal (
    binary_string                             varchar2
  ) return pls_integer
  as
   l_binary_string                            varchar2(32000 char) := binary_string;
   l_decimal                                  pls_integer := 0;
   l_current_char                             char(1);

  begin  
     while length(l_binary_string) >= 1
     loop
        l_decimal := l_decimal * 2; -- moving one char in binary string means multiplication by 2
        l_current_char := substr(l_binary_string,1,1);
        l_binary_string := substr(l_binary_string,2);
        if l_current_char = '1'
        then
           l_decimal := l_decimal + l_current_char; -- add current char, if '1'
        elsif l_current_char != '0'
        then
            return 0;
        end if;
     end loop;
     
     return l_decimal;
     
  exception 
     when others 
       then raise;
  end to_decimal;
   

end binary#;
/

Community comments

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Avatar of chezwicker

Oh, seems I forgot to mention something: you could just user for i in reverse 1 .. length(l_binary_string) loop to save getting a substring and instead use substr(l_binary_string, i, 1).

And just on a side note on performance: you're now doing an implicit conversion between char and numeric. Adding the constant 1 should be faster (ok, that's really nitpicking now ;-)

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?