The modified Example Program:

! MExample Program 7-3

! Calculate the value of a factorial number.

! Display values for n = 1 to 10, use color and sound to distinguish between

! different types of errors and the result of valid calculations.

! Input data -1,3.3,1,2,3,4,5,6,7,8,9,10 from a data statement

! in a do loop to test the behaviour of the modified program.

! Run do trace, slow (Number) to watch how the program works.

DECLARE FUNCTION Factorial

!INPUT prompt "Enter number: ": Number

DO while more data

READ Number

IF Number < 0 then

SET COLOR "red"

SOUND 500,.3

PRINT "The number must be positive or zero."

ELSEIF Number <> Int(Number) then

SET COLOR "green"

SOUND 300,.3

PRINT "The number must be an integer."

ELSE

SOUND 1000,0.1

SET COLOR "blue" ! blue for a valid factorial calculation

PRINT "The factorial value of"; Number;

PRINT "is"; Factorial(Number)

END IF

LOOP

DATA -1,3.3,1,2,3,4,5,6,7,8,9,10

END

FUNCTION Factorial (X)

! Calculate the factorial value of parameter X.

LET Result = 1 ! initialize the variable Result

FOR I = 1 to X

LET Result = Result * I

NEXT I

LET Factorial = Result

END FUNCTION

The output of the modified program:

The number must be positive or zero.

The number must be an integer.

The factorial value of 1 is 1

The factorial value of 2 is 2

The factorial value of 3 is 6

The factorial value of 4 is 24

The factorial value of 5 is 120

The factorial value of 6 is 720

The factorial value of 7 is 5040

The factorial value of 8 is 40320

The factorial value of 9 is 362880

The factorial value of 10 is 3628800