About this task
Some of the built-in functions provide a convenient way
to test input. When
a program uses
input, the user might provide input that is not valid. For instance,
in the example of using comparison expressions in section
Using Comparison Expressions, the
program uses
a dollar amount in the following instruction.
PARSE PULL yesterday /* Gets yesterday's price from input stream */
If the
program pulls
only a number, the
program processes
that information correctly. However, if the
program pulls
a number preceded by a dollar sign or pulls a word, such as
nothing, the
program returns
an error. To avoid getting an error, you can check the input with
the DATATYPE function as follows.
IF DATATYPE(yesterday) \= 'NUM'
THEN DO
SAY 'The input amount was in the wrong format.'
EXIT
END
Other useful built-in functions to test
input are WORDS, VERIFY, LENGTH, and SIGN.