(* Divide an integer by a natural number, using operations of
addition, subtraction , doubling and halving only. Repeat
reading pairs of integers, until you encounter a 0. For each pair,
print dividend, divisor, quotient, and remainder. Indicate
invariant of loop.*)
MODULE divide;
FROM Terminal IMPORT WriteString, WriteLn;
FROM InOut IMPORT ReadInt,WriteInt;
VAR a,b,q,r:INTEGER;
PROCEDURE divide(x,y: INTEGER; VAR z,a:INTEGER);
VAR q,r,w: INTEGER;
BEGIN
r := x; w := y; q := 0;
WHILE w <= r DO w := 2*w END;
WHILE w # y DO
w := w DIV 2;
q := 2*q;
IF w <= r THEN
r := r-w; INC(q);
END
END;
z := q; a := r;
END divide;
BEGIN
WriteString('Enter dividend> ');
ReadInt(a);
WHILE a # 0 DO
WriteString('Enter divisor> ');
ReadInt(b);
divide(a,b,q,r);
WriteInt(a,3); WriteInt(b,3);
WriteInt(q,3); WriteInt(r,3);
WriteLn;
WriteString('Enter dividend> ');
ReadInt(a);
END
END divide.
