Commodore Plus 4 - Page 48

36 The BASIC Language
You can have a conditional clause (WHILE or UNTIL) in both the DO and
LOOP commands in one loop.
If you omit both UNTIL and WHILE clauses in the DO loop, the loop is an
infinite loop: it continues executing without stopping. You must interrupt the
program with the STOP key to terminate the loop.
3. EXIT lets you leave the loop before the UNTIL or WHILE conditions end
the loop. You can, for example, use EXIT to check for unwanted values and end a
loop if a particular value is encountered. After an EXIT command, program
execution passes to the line following the LOOP command.
Note: Always use EXIT (never GOTO) to leave a loop prematurely.
Example: 5 DATA YES, NO, YES, NO, END Lists DATA values.
10 DO WHILE X < 50 Begins a loop that runs as long as
X is less than 50.
SO X = X + 1 Increments the counter for the
WHILE clause.
30 READ ANSI Reads data from line 5.
40 IF ANSI = "END" THEN EXIT Aborts the loop if ANS$ = END.
50 LOOP Sends the loop back to DO.
NEW Clears the previous program.
10 D0:PRINT "HALT!" Begins a DO loop.
SO X = X + 1 Adds 1 to X each time the loop
executes.
30 IF X = 25 THEN EXIT Aborts the loop when X = 25.
40 LOOP Sends the loop back to DO.
4. LOOP works with DO to set conditions for a repeated sequence of program
lines. LOOP works for DO as NEXT does for FOR: it marks the end of the loop
and sends execution back to the beginning of the loop.
If you do not include an UNTIL or WHILE clause with the DO command, you
can add one here. The UNTIL and WHILE commands can appear with either the
DO command or the LOOP command, or both.
DRAW Abbr.dR
DRAW color source, coordinates TO coordinates TO coordinates etc.
Draws dots, lines, and any angled shape. DRAW can be used only in one of the
graphic modes. Though you can draw any polygon with DRAW, it is sometimes
simpler to use CIRCLE to draw polygons with regular-length sides. See Chapter
4 for more information on DRAW coordinates.