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Chapter 14 - Qbasic Tutorial

That last program works great, as long as the user always types in a lowercase "y". What happens if the user types in "yes"? Since "yes" is not the same as "y" to the computer, the test for Answer$="y" will fail, and the program will end. Probably not a good idea. We have the same problem if our user enters a capital "Y". Try a few of these to see what I mean.

There are several ways to make this program smarter and easier to use for our users. We could have it check for a few different ways of saying yes by using "OR", like this:

 CLS
DO
INPUT "Enter the first number: ", A
INPUT "Enter the second number: ", B
PRINT "The answer is: "; A * B

INPUT "Would you like to do it again (y/n)? ", Answer$
LOOP WHILE Answer$="y" OR Answer$="Y"

This version will allow the user to enter "y" or "Y" and the program will run again. We can get even more clever by using LEFT$ like this:

 CLS
DO
INPUT "Enter the first number: ", A
INPUT "Enter the second number: ", B
PRINT "The answer is: "; A * B

INPUT "Would you like to do it again? ", Answer$
FirstLetter$ = LEFT$(Answer$, 1)
LOOP WHILE FirstLetter$="y" OR FirstLetter$="Y"

This version will let the user enter "Yes", "yes", or just about anything that starts with a "y" because LEFT$ is used to only look at the first character in their answer. You could even enter "yep" or "YEAH!" and the program will begin again.

This may seem to make the computer smarter, but we know what's really going on. To prove the computer really isn't very smart, try entering "sure" or "yellow". It thinks "sure" is "no", and "yellow" is "yes".

LEFT$

LEFT$ can be used to take a certain number of letters from the left side of a string variable. As an example, if we have:

 A$="TEST"

Then LEFT$(A$,2) will give us "TE". LEFT$(A$,3) will give us "TES". The first "parameter" you pass to LEFT$ is the string you want to work with. The second parameter you pass to LEFT$ is the number of characters (letters) you want. Let's try a program that uses LEFT$ in a different way:

 INPUT "Enter something:", A$
PRINT A$
PRINT LEFT$(A$,1)
PRINT LEFT$(A$,2)
PRINT LEFT$(A$,3)

This program will print the first character of whatever you enter, followed by the first two characters, followed by the first three characters:

 Enter something: Jack
Jack
J
Ja
Jac

QBASIC also provides a RIGHT$() in case you were curious, and it works just like LEFT$(). Try this:

 INPUT "Enter something:", A$
PRINT A$
PRINT RIGHT$(A$,1)
PRINT RIGHT$(A$,2)
PRINT RIGHT$(A$,3)

Here's an example of what that program will do:

 Enter something: Jack
Jack
k
ck
ack


Source: http://jpsor.ucoz.com
Category: Qbasic Tutorial | Added by: JPSor (2009-02-26) | Author: JPSor
Views: 670 | Rating: 5.0/1 |
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