# Binary to Decimal in Delphi 7

I'm trying to do a simple console program where user input a binary string and he get a decimal number. I dont need to check if the binary string have something else than 0 or 1. I already managed to do decimal to binary but can't do it the other way.

I tried some code found on SO and Reddit but most of the time i got error I/O 105

Here's the dec to bin :

``````program dectobin;

{\$APPTYPE CONSOLE}

uses
SysUtils,
Crt32;

var
d,a :Integer;
str :String;

begin
str:='';
while a>0 do begin
d:=a mod 2;
str:=concat(IntToStr(d),str);
a:=a div 2;
end;
Writeln(str);
end.```
``````

On Best Solutions

Basics of positional number systems (PNS)

• The number of unique digits in a PNS is its base (or radix)
• The decimal system (base = 10) has ten digits, 0..9
• The binary system (base = 2) has two digits, 0..1
• The position of a digit in a number determines its weight:
• the rightmost digit has a weight of units (1), (base)^0 (decimal 1, binary 1)
• the second (from right) digit has a weight of (base)^1 (decimal 10, binary 2)
• the third (from right) digit has a weight of (base)^2 (decimal 100, binary 4)
• and so on ....

Note that the weight is always `base * weight of previous digit` (in a right to left direction)

General interpretation of a string of numbers in any positional number system

``````  assign a variable 'result' = 0
assign a variable 'weight' = 1 (for (base)^0 )
repeat
read the rightmost (not yet read) digit from string
convert digit from character to integer
multiply it by weight and add to variable 'result'
multiply weight by base in prep. for next digit
until no more digits
``````

After previous, you can use e.g. `IntToStr()` to convert to decimal string.