Answer:

' Draw 10 Red Balloons each with a GREEN string
' The balloons hover above the   brown earth.
SCREEN 12                    ' start up graphics
'
LET BALLOON = 1              ' start with balloon number 1
DO WHILE BALLOON <= 10       ' end with balloon number 10
  LET X = BALLOON * 64 - 32  ' calculate an X for this balloon
'
  COLOR 4                    ' set the pen color to red
  CIRCLE (X, 100), 25        ' draw a balloon
'
  COLOR 2                    ' set the pen color to green
  LINE  (X, 125) - (X,225)   ' draw its string
  LET BALLOON = BALLOON + 1  ' go on to next balloon
LOOP
'
COLOR 6                      ' set the pen color to brown
LINE (0, 240)-(639,240)      ' draw a line across the screen
END

You could have drawn the line first, before all the balloons. This would be fine. It would be a mistake to put it inside the loop (between the DO and the LOOP) since this would draw it again and again, needlessly.

SLEEP

(the program, not you)

You may think this program is getting to be a bit overblown. But let's make one more addition, then we'll be done. It would be nice to put a little action into the picture. In a later chapter we will do much more of this, but right now it is easy to add one statement that makes the program more interesting.

The SLEEP statement tells the computer to do nothing for a few seconds:

SLEEP  numberOfSeconds

For example, look at the following program:

'  Sleep for a while after each arithmetic statement
'
LET  VALUE = 45          ' put 45 in VALUE
SLEEP 2                  ' do nothing for two seconds
LET  EXTRA = 25          ' put 25 in EXTRA
SLEEP 10                 ' do nothing for 10 seconds
LET SUM = VALUE + EXTRA  ' add VALUE plus EXTRA and put the result in SUM
SLEEP 5                  ' do nothing for 5 seconds
PRINT "That was Hard!  The sum is:", SUM            ' write out the result
END

The example program is silly; there is no good reason for using the SLEEP statements in it (except maybe to make it look like the computer took lots of time to solve this hard problem!)

An interesting place for the SLEEP statement is in the balloon program. If the computer did nothing for one second after drawing each balloon and string, you would see the picture "unfold" as it was being created.

QUESTION 25:

Here is the program so far:

' Draw 10 Red Balloons each with a GREEN string
' The balloons hover above the  brown earth.
SCREEN 12                    ' start up graphics
'
LET BALLOON = 1              ' start with balloon number 1
DO WHILE BALLOON <= 10       ' end with balloon number 10
  LET X = BALLOON * 64 - 32  ' calculate an X for this balloon
'
  COLOR 4                    ' set the pen color to red
  CIRCLE (X, 100), 25        ' draw a balloon
'
  COLOR 2                    ' set the pen color to green
  LINE  (X, 125) - (X,225)   ' draw its string
  LET BALLOON = BALLOON + 1  ' go on to next balloon
LOOP
'
COLOR 6                      ' set the pen color to brown
LINE (0, 240)-(639,240)      ' draw a line across the screen
END

Modify the program by adding one SLEEP statement so that the program does nothing for one second after drawing each balloon-and-string. Consider carefully where the statement should go.