PROGRAM Calculator (Input,Output);

{ Program to read and evaluate an arithmetic expression with one operator.}

VAR
   Operand1, Operand2 : Real;
   Result : Real;
   Operator : Char;


BEGIN
   Writeln('Enter a binary arithmetic expression.');
   Writeln('Use + - * / as operator');
   Readln(Operand1,Operator,Operand2);

   IF (Operator <> '+') AND
      (Operator <> '-') AND
      (Operator <> '*') AND
      (Operator <> 'x') AND
      (Operator <> '/') THEN
         Writeln('Invalid operator.  Must be + - * / only.')
   ELSE
     Begin
       IF Operator = '+' THEN
          Result := Operand1 + Operand2

       ELSE IF Operator = '-' THEN
          Result := Operand1 - Operand2

       ELSE IF (Operator = '*') OR (Operator = 'x') THEN
          Result := Operand1 * Operand2

       ELSE IF Operator = '/' THEN
          IF Operand2 <> 0 THEN
             Result := Operand1 / Operand2
          ELSE
             Writeln('No division by zero');

       Writeln('= ',Result:1:4);
     End;
END.