Program to illustrate exchange of values between two variables.
Also introduces assignment of string constants to string variables
and writeln statements with multiple arguments separated by commas.

	program exc;
	var
		x, y, t: string;
	begin
	x := 'tomato';
	y := 'blueberry');
	writeln('x = ', x, ' y = ', y);
	writeln('exchange');
	t := x;
	x := y;
	y := t;
	writeln('x = ', x, ' y = ', y);
	readln;
	end.

Sample output
>x = tomato y = blueberry
>x = blueberry y = tomato