A positive integer is entered from the keyboard. Calculate the sum of odd digits. (Pascal)

program calc;
var a, sum, k, code: integer;
// a – number, sum – the sum of odd digits,
// k is the position of the digit in the number, code is the error message.
s, s1: string; // s is a string of digits and s1 is a substring of digits at position k.
begin
writeln (‘Enter an integer’);
read (a); // enter a number
str (a, s); // converting numbers to string
sum: = 0;
for i: integer: = 1 to length (s) do
begin
s1: = copy (s, i, 1); // highlight a single digit
val (s1, k, Code); // convert a string-digit to a number
if k mod 2 = 1 then sum: = sum + k; // parity check and sum of odd digits
end;
writeln (‘The sum of odd digits is equal to’, sum)
end.