Atari 800

68 User's Handbook to the Atari 400/ 800 Computers
loops is to end an outer loop before an inner loop is ended. Also,
be certain that that every NEXT statement has a matching FOR
statement. If the Atari BASIC int erpreter cannot match every
NEXT statement with a preceding FOR statement, an error will
result.
Conditional Statements
One of the most important features of a computer is its ability to
make a decision. BASIC uses the IF, THEN, ELSE statement to take
advantage
of the computer's decision making ability. The IF ,
THEN,
ELSE statement takes the following form:
IF expression THEN statement ELSE statement
The IF statement sets up a question or a condition. If the answer
to that question is true, the statement following THEN is
executed. If the answer is false, the statement following ELSE will
be executed.
In the following example, if X is equal to 0, then Y will be set to 1.
If X is not equal to 0, Y will be set to O.
100 IF X = 0 THEN Y = 1 ELSE Y = 0
The IF, THEN, ELSE statement may be shortened to just IF, THEN
as shown below.
050 Y = 0
100 IF X = 1 THEN Y = 1
In this example, if X is equal to 1, the statement following THEN
will be executed . If X is not equal to 1, program execut ion will
continue with the next program statement (in our examp le--line
200).
Branching Statements
Branching statements change the execution pattern of programs
from their usual line by line execution in ascending line number
order. A branching statement allows program control to be