Radio Shack TRS-80 Model 3 - Page 171

THEN statementor line number
Initiates the" action clause" of an IF-THEN type statement. THEN is optional except
when it is required to eliminate an ambiguity, as in
IF A< 0100. THEN should be
used in
IF-THEN-ELSE statements.
ELSE statement or line number
Used after IF to specify an alternative action in case the IF test fails. (When no ELSE
statementis used, control falls through to the next program line aftera test fails.)
Examples:
100 INPUT AS: IF AS = "YES" THEN 300 ELSE END
In line 100, if A$ equals "YES" then the program branches to line 300. But if A$
does not equal' 'YES" , program skips over to the ELSE statement which then
instructs the
Computer to end execution.
20~~ I F' t~ < B "rHE:N PI~ I NT "ti<l3
11
FL..BE: pr~ I N'r "P,<:::~l~ II
If Ais less than B, the Computerprints that fact, and then proceeds down to the next
programline,
skipping the ELSE statement. If Ais not less than B, Computer jumps
directly to the ELSE statementand prints the specified message. Then control
passes to the next statementin the program.
200 IF A>"001 THEN B = 1/A: A = A/S: ELSE 260
If A> .001 is True, then the nexttwo statements will beexecuted, assigning new
values to
Band A. Then the program will drop down to the next line, skipping the
ELSE statement. But if A> .001 is False, the program jumps directly over to the
ELSE statement, which then instructs it to branch to line 260. Note that GOTO is not
required after
ELSE.
IF-THEN-ELSE statements may be nested, butyou have to take care to match up the
IFs and ELSEs.
810 INPUT "ENTER TWO NUMBERS"; A, B
820 IF A <= B THEN IF A < B PRINT A;: ELSE PRINT "NEITHER
";: ELSE PRINT B;
830 PRINT "IS SMALLER"
840 END
RUN the program, inputting various pairs of numbers. The program picks out and
prints the smaller
of any two numbers youenter.
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