Conditions

About Conditions

In GCBASIC (and most other programming languages) a condition is a statement that can be either true or false. Conditions are used when the program must make a decision. A condition is generally given as a value or variable, a relative operator (such as = or >), and another value or variable. Several conditions can be combined to form one condition through the use of logical operators such as AND and OR.

GCBASIC supports these relative operators:

Symbol Meaning

=

Equal

<>

Not Equal

<

Less Than

>

Greater Than

⇐

Less than or equal to

>=

Greater than or equal to

In addition, these logical operators can be used to combine several conditions into one:

Name Abbreviation Condition true if

AND

&

both conditions are true

OR

|

at least one condition is true

XOR

#

one condition is true

NOT

!

the condition is not true

NOT is slightly different to the other logical operators, in that it only needs one other condition. Other arithmetic operators may be combined in conditions, to change values before they are compared, for example.

GCBASIC has two built in conditions - TRUE, which is always true, and FALSE, which is always false. These can be used to create Conditional tests and infinite loops.

The condition bit_variable = TRUE is treated as TRUE if the bit is on.  Any non-zero value will be treated as equal to a high bit. The condition bit_variable = other_type_of_variable generates a warning.  If the byte_variable is set to TRUE and then compared to the bit, it will always be FALSE because the high bit will be treated as a 1.  But the new warning will be generated, "Comparison will fail if %nonbit% is any value other than 0 or 1"

It is also possible to test individual bits in conditions. To do this, specify the bit to test, then 1 or 0 (or ON and OFF respectively). Presently there is no way to combine bit tests with other conditions - NOT, AND, OR and XOR will not work.

Example conditions:

Condition Comments

Temp = 0

Condition is true if Temp = 0

Sensor <> 0

Condition is true if Sensor is not 0

Reading1 > Reading2

True if Reading1 is more than Reading2

Mode = 1 AND Time > 10

True if Mode is 1 and Time is more than 10

Heat > 5 OR Smoke > 2

True if Heat is more than 5 or Smoke is more than 2

Light >= 10 AND (NOT Time > 7)

True if Light is 10 or more, and Time is 7 or less

Temp.0 ON

True if Temp bit 0 is on

Constraints when using Conditional Test

As GCBASIC is very flexible with the use of variables type this can cause issues when testing constants and/or functions.

A few simple rules. Always put the function or constant first, or, always call the function with the addition of the braces.

The example code below shows the correct method and an example that does compile but will not work as expected.

    'Example A - works
    'Call the function by adding the braces
    '
    Do
    Loop While HSerReceive() <> 62

    'Example B - works
    'Please the constant first - this is the general rule - put the constant first.
    '
    Do
    Loop While 62 <> HSerReceive

This fails as the function will not be called

    'Example C - compiles but does not operate as expected
    Do
    Loop While HSerReceive <> 62






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