Smart BASIC Programming. Lesson 4

[Mr. Kibernetik]

Lesson 4 - Logics

Often it is needed to perform an action only if some conditions are fulfilled. And IF THEN ELSE command serves this purpose.

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INPUT N
PRINT "Number";N;
IF EVEN (N) = 1 THEN PRINT "is even" ELSE PRINT "is odd"

IF THEN ELSE command can be written in several lines:

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INPUT A,B
IF A < B THEN
  PRINT A;"is less than";B
ELSE
  IF A = B THEN
    PRINT A;"is equal to";B
  ELSE
    PRINT A;"is greater than";B
  END IF
END IF

It is a bulky example, but it shows that conditions could be of any complexity.

IF THEN ELSE is working like that: after IF there is a condition. If this condition is true then code after THEN is executed. If condition is false then code after ELSE is executed. Also ELSE part can be absent, so it could be written like that:

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INPUT A,B
IF A < B THEN PRINT A;"is less than";B
IF A > B THEN PRINT A;"is greater than";B
IF A = B THEN PRINT A;"is equal to";B

Number instead of condition can be used. If number is zero then condition is considered to be false. If number is not zero then condition is true. So, first example could be written like that:

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INPUT N
PRINT "Number";N;
IF EVEN (N) THEN PRINT "is even" ELSE PRINT "is odd"

Conditions can include logical operations AND, OR and NOT. Operation NOT inverts the result when using number.

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INPUT X,Y
IF X > 0 OR Y > 0 THEN PRINT "At least one number is greater than zero"
IF X > 0 AND Y > 0 THEN PRINT "Both numbers are greater than zero"

EXERCISE 5
Write a program which fills the screen with random circles when device is oriented horizontally and with random lines when device is oriented vertically.