PicoMite User Manual

The IF Statement

Making decisions is at the core of most computer programs and in BASIC this is usually done with the IF statement. This is written almost like an English sentence:

IF condition THEN action

The condition is usually a comparison such as equals, less than, more than, etc.

For example:

IF Temp < 25 THEN PRINT "Cold"

Temp would be a variable holding the current temperature (in ºC) and PRINT "Cold" the action to be done.

There are a range of tests that you can make:

You can also add an ELSE clause which will be executed if the initial condition tested false:

IF condition THEN true-action ELSE false-action

For example, this will execute different actions when the temperature is under 25 or 25 or more:

IF Temp < 25 THEN PRINT "Cold" ELSE PRINT "Hot"

The previous examples all used single line IF statements but you can also use a multiline IF statement.

They look like this:

IF condition THEN
true-action
true-action
ENDIF

or

IF condition THEN
true-action
true-action
ELSE
false-action
false-action
ENDIF

Unlike the single line IF statement you can have many true actions with each on their own line and similarly many false actions. Generally the single line IF statement is handy if you have a simple action that needs to be taken while the multiline version is much easier to understand if the actions are numerous and more complicated.

An example of a multiline IF statement with more than one action is:

IF Amount < 100 THEN
PRINT "Too low"
PRINT “Minimum value is 100”
ELSE
PRINT "Input accepted"
SaveToSDCard
PRINT "Enter second amount"
ENDIF

Note that in the above example each action is indented to show what part of the IF structure it belongs to. Indenting is not mandatory but it makes a program much easier to understand for someone who is not familiar with it and therefore it is highly recommended.

In a multiline IF statement you can make additional tests using the ELSE IF command. This is best explained by using an example (the temperatures are all in ºC):

IF Temp < 0 THEN
PRINT “Freezing”
ELSE IF Temp < 20 THEN
PRINT “Cold”
ELSE IF Temp < 35 THEN
PRINT “Warm”
ELSE
PRINT “Hot”
ENDIF

The ELSE IF uses the same tests as an ordinary IF (ie, <, <=, etc) but that test will only be made if the preceding test was false. So, for example, you will only get the message Warm if Temp < 0 failed, and Temp < 20 failed but Temp < 35 was true. The final ELSE will catch the case where all the tests were false.

An expression like Temp < 20 is evaluated by MMBasic as either true or false with true having a value of one and false zero. You can see this if you entered the following at the console:

PRINT 30 > 20

MMBasic will print 1 meaning that the value of the expression is true.

Similarly the following will print 0 meaning that the expression evaluated to false.

PRINT 30 < 20

The IF statement does not really care about what the condition actually is, it just evaluates the condition and if the result is zero it will take that as false and if non zero it will take it as true.

This allows for some handy shortcuts. For example, if BalanceCorrect is a variable that is true (non zero) when some feature of the program is correct then the following can be used to make a decision based on that value:

IF BalanceCorrect THEN …do something…