Sharp PC-1500A Instruction Manual page 47

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Program Listing:
10 PAL.iSE "AAE YOU ASLEEP?"
20 INPUT "TYPE YES OR NO "; SXS
30
IF SX$ = "YES" THEN PRINT "OH. SORRY TO
DISTURB YOU"
4 0 END
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This soporific program will only produce output if you answer affirmatively. The general fo rm
of the IF statement. which
lin~ 30
illustrates. is:
IF condition THEN statement
During execution. the test embedded in the IF clause is performed. Whether the statement is
performed, or not, depends on the result of the test. The test is usually an inequality and is called
a " condition." Remember that inequalities are comparisons which are either True or
False.
If
the inequality is True then th., statement is executed. If the inequality is False then the statement
is skipped.
In our sample program the test is whether the variable SXS is equal to (contains) the character
string "YES". If it does. and o nly if it does, then the PRINT instruction is followed. If SXS is not
equal to "YES", then the PRINT instruction is ignored. In either case. no matter whether the PR INT
statement is executed or ignored, SHARP will proceed, as normal . to the next line. (I n our sample
program the next line is line 40) .
Notice that we could have reversed our te.t by altering several lines in the following manner:
30
IF SXS =" NO" THEN END
40 PRINT "OH, SORRY TO DISTURB YOU"
This progn.lm, however. is not quite the same as the o riginal. It allows our apologetic computer
to
talk
with anyone who mistypes
or
who doesn't answer with a
" NO". In addition.
this
pro g ran'I
really has two endpoints; the END statement in line 30 and the implied END beyond line 40.
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45