Here's an old school IF statement for you, but there is a problem

Question

I have an IF statement in QBASIC... yes... QBASIC...

I have been teaching someone to program (I decided this would be nice and easy to see how the syntax works).

...Anyway, I have this code:

CLS

start:
INPUT ">>", a$

PRINT a$
IF (INSTR(a$, "do you")) THEN
    IF (INSTR(a$, "like")) THEN
        IF (INSTR(a$, "cheese")) THEN PRINT "Yep, I like cheese":
        IF (INSTR(a$, "music")) THEN PRINT "Depends, which genre?": GOTO musicGenre
    ELSE IF (INSTR(a$, "hate")) THEN
            IF (INSTR(a$, "cheese")) THEN PRINT "No, I like cheese"
        END IF
    END IF
END IF


musicGenre:
INPUT ">>", m$
SELECT CASE (m$)
    CASE "pop"
        PRINT "..pop! lol, baa baa"
    CASE "rock"
        PRINT "Rock is ok"
END SELECT
GOTO start

But when I type "do you like cheese?" it seems to only reply "Yep, I like cheese" every other time...

Could anyone shed some light on this?

note:
"do you like music?" works every time...

note 2:
Screenshot of the output:
alt text

What is the incorrect output you see when you input "do you like cheese?" and it doesn't say "Yep, I like cheese"? — Steven, Sep 16 '10 at 13:01
What does it say when it doesn't say "Yep, I like cheese" as expected? Anything, or nothing? — Meff, Sep 16 '10 at 13:02
InStr returns an index as far as I know... Are you sure that the value it returns on failure is evaluated as false? I don't know QBasic, but I did stuff in VB6... — apirogov, Sep 16 '10 at 13:04
Is it exactly every other time or apparently somewhat random. My first thought is make sure you aren't misspelling your input. — Steven, Sep 16 '10 at 13:05
You are using input to parse cheese then a second input which does not. — eoredson, Aug 27 '16 at 02:31

Steven · Accepted Answer · 2010-09-16T13:23:36.697

4

Your code you provided appears correct.

Try one of the following:

If possible, send us a larger code sample. I'm guessing the error is outside the code you provided.
Output the input (a$) before the first IF to confirm your code will be working with the expected input.
In most languages, FALSE is zero and true is anything else. However, you may want to be more explicit with the following IF (INSTR(a$) > 0).

EDIT: You should put a goto start on any cheese result. Otherwise, it's going to the musicGenre code.

edited Sep 16 '10 at 13:23

answered Sep 16 '10 at 13:15

Steven

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Hey, cheers very much. a$ outputs as "`do you like cheese`" **however**, it won't even output the a$ afterwards.. like.. the output is right the first time, then it is empty (including the outputted a$) the second time, then it's correct the third. – Barrie Reader Sep 16 '10 at 13:21

score 2 · Answer 2 · edited Jul 06 '13 at 22:29

2

CLS

start:
    INPUT ">>", a$

    IF (INSTR(1, a$, "do you")) THEN
        IF (INSTR(1, a$, "like")) THEN
            IF (INSTR(1, a$, "cheese")) THEN PRINT "Yep, I like cheese"
            IF (INSTR(1, a$, "music")) THEN PRINT "Depends, which genre?": GOSUB musicGenre
        END IF
    IF (INSTR(1, a$, "hate")) THEN
        IF (INSTR(1, a$, "cheese")) THEN PRINT "No, I like cheese"
    END IF
END IF

GOTO start
musicGenre:
    INPUT ">>", m$
    SELECT CASE (m$)
        CASE "pop"
            PRINT "..pop! lol, baa baa"
        CASE "rock"
            PRINT "Rock is ok"
    END SELECT
RETURN

edited Jul 06 '13 at 22:29

Wookie88

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answered Jul 06 '13 at 22:10

Michael

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Code without any explanation isn't an acceptable answer here. Please [edit] to provide some information about **how** your code solves the problem. Thanks. – Ken White Jul 06 '13 at 22:39

score 0 · Answer 3 · answered Aug 27 '16 at 02:40

This program demonstrates parsing input and gosubs in Basic.

REM Cheese progran source:
CLS
DO
    INPUT ">>", a$
    a$ = LCASE$(a$)
    PRINT a$
    IF INSTR(a$, "do you") THEN
        IF INSTR(a$, "like") THEN
            IF INSTR(a$, "cheese") THEN
                PRINT "Yep, I like cheese":
            END IF
            IF INSTR(a$, "music") THEN
                PRINT "Depends, which genre?"
                GOSUB MusicGenre
            END IF
        ELSE
            IF INSTR(a$, "hate") THEN
                IF INSTR(a$, "cheese") THEN
                    PRINT "No, I like cheese"
                END IF
            END IF
        END IF
    END IF
LOOP
END
MusicGenre:
INPUT ">>>", m$
a$ = LCASE$(a$)
SELECT CASE (m$)
    CASE "pop"
        PRINT "..pop! lol, baa baa"
    CASE "rock"
        PRINT "Rock is ok"
END SELECT
RETURN

Here's an old school IF statement for you, but there is a problem

3 Answers3