Prolog first lab

lab_1.pr

predicates
	nondeterm solve(real, real, real)
	nondeterm reply(real, real, real)
	nondeterm print_complex(real, real)
	nondeterm run
	nondeterm do(char)
	
	clauses
		solve(A,B,C):-
			A=0 AND B=0 AND C<>0,
			write("NO solution"), nl.
		solve(A,B,C):-
			A=0 AND B=0 AND C=0,
			write("x is any real number"), nl.
		solve(A,B,C):-
			A=0,
			X=-C/B,write("x=",X),nl.
		solve(A,B,C):-
			D=B*B-4*A*C,
			reply(A,B,D).
		reply(A,B,D):-
			D<0,
			R=-B/(2*A),
			I1=sqrt(abs(D))/(2*A),
			I2=-sqrt(abs(D))/(2*A),
			write("x1="),print_complex(R,I1),nl,
			write("x2="),print_complex(R,I2),nl.
		reply(A,B,D):-
			D=0,
			X=-B/(2*A), write("x=", X).
		reply(A,B,D):-
			X1=(-B+sqrt(D))/(2*A),
			X2=(-B-sqrt(D))/(2*A),
			write ("x1=",X1,",x2=", X2), nl.
		print_complex(R,I):-
			I<0,
			write(R,I,"*i").
		print_complex(R,I):-
			I>=0,
			write(R,"+",I,"*i").
		run:-
			write("Enter\n"),
			write("-1 to solve quadratic equation\n"),
			write("     ax^2+bx+c=0\n"),
			write("-0 to EXIT\n"),
			write("*************\n"),
			write(">>"), readchar(X), write(X), nl,
			do(X),
			run.
		do('1'):-
			write("a="), readreal(A), A<>0, nl,
			write("b="), readreal(B), nl,
			write("c="), readreal(C), nl,
			solve(A,B,C).
		do('0'):-
			write("That's all"), exit.
		do(_):-
			write("bad value"), nl.
	goal run.