VFP Tutorial - Do Case
The Do Case structure allows a choice between
several actions based on the result of a logical expression:
Do Case
Case _TALLY = 0
Wait Window
'No records found'
Case _TALLY = 1
Wait Window
'One record found'
Otherwise
Wait Window
'Many records found'
EndCase
Each Case statement is followed
by an expression which must evaluate to true or false. FoxPro
evaluates each of these in sequence.
If the expression following the first
Case statement evaluates as true
(.T. in FoxPro) then the statements
between this Case and the next one
will be executed. The rest of the structure will be skipped
and execution will continue on the line following the
EndCase statement.
If the first expression evaluates as false
(.F. in FoxPro) then the next
Case statements will be evaluated in
turn until one is found to be true. If none are found to be true
then the code following Otherwise
will be executed.
Notes
_TALLY is a variable maintained by
FoxPro which holds the number of records processed by the last
command. It is very useful in situations like this where you
need to know how many records have been found.
Each logical condition must evaluate as either
.T.
or
.F.
because the logical values in FoxPro are a separate data type.
Unlike in many other languages, an integer result will not be
interpreted as a logical value.
Be careful to get the tests in the right order when designing a
Case structure. Remember that the
expressions are evaluated in sequence and put the toughest test
first. If for example you need to test whether something is
greater than 1 or greater than 10 then you must test for greater
than 10 first. If you test for greater than 1 first then a value
such as 11 would pass that test and the greater than 10 test would
never be reached. This sort of mistake can be difficult to detect
in tests because the program runs without error and will give the
right result most of the time.
The Otherwise clause is optional. If
it is not included and all the individual
Case statements evaluate as false
then none of the code will be executed.
It is good practice to include an Otherwise
clause even if there is no action which needs to be taken. If you are
positive that the individual Case statements
cover every possible situation then add an
Otherwise and display an error message.
Each Case can have an expression
based on a different variable. This example works out the method
of delivery from the value of the order, the weight of the goods
and the country to which it has to be delivered.
Do Case
Case
lyCost > 1000
lcDelMethod = 'Free'
Case
lnWeight > 10
lcDelMethod = 'Collect'
Case
lcCountry <>
'UK'
lcDelMethod = 'Airmail'
Otherwise
lcDelMethod = '2nd class mail'
EndCase
Back to FoxPro
program control
structures.
Introduction |
Environment |
Project |
Tables |
Forms |
Navigation |
Executable
|