...
caseListn: statementn;
end
where
selectorExpression is any expression of an ordinal type (string types are invalid) and each
caseList is one of
the following:
A numeral,
declared constant, or other expression that the compiler can evaluate without executing your
program. It must be of an ordinal type compatible with
selectorExpression. Thus
7
, True,
4 + 5 * 3
, 'A', and
Integer('A')
can all be used as
caseLists, but variables and most function calls cannot. (A few built-in
functions like
Hi
and
Lo
can
occur in a caseList. See Constant expressions.)
A subrange having the form
First..Last, where
First and
Last both satisfy the criterion above and
First is less
than or equal to
Last.
A
list having the form item1, ..., itemn, where each
item satisfies one of the criteria above.
Each value represented by a
caseList must be unique in the case statement; subranges and lists cannot overlap. A
case statement can have a final else clause:
case selectorExpression of
caseList1: statement1;
...
caselistn: statementn;
else
statements;
end
where
statements is a semicolon-delimited sequence of statements. When a case statement is executed, at most
one of
statement1 ... statementn is executed. Whichever
caseList has
a value equal to that of selectorExpression
determines the statement to be used. If none of the
caseLists has the same value as
selectorExpression, then the
statements in the else clause (if there is one) are executed.
The
case statement
case I of
1..5: Caption := 'Low';
6..9: Caption := 'High';
0, 10..99: Caption := 'Out of range';
else
Caption := '';
end
is equivalent to the nested conditional
if I in [1..5] then
Caption := 'Low';
else if I in [6..10] then
Caption := 'High';
else if (I = 0) or (I in [10..99]) then
Caption := 'Out of range'
else
Caption := '';
Other examples of case statements
38
case MyColor of
Red: X := 1;
Green: X := 2;
Blue: X = 3;
Yellow, Orange, Black: X := 0;
end;
case
Selection of
Done: Form1.Close;
Compute: calculateTotal(UnitCost, Quantity);
else
Beep;
end;
Control Loops
Loops allow you to execute a sequence of statements repeatedly, using a control condition or variable to determine
when the execution stops. Delphi has three kinds of control loop: repeat statements, while statements, and for
statements.
You can use the standard
Break
and
Continue
procedures to control the flow of a repeat, while, or for statement.
Break
terminates the
statement in which it occurs, while
Continue
begins executing the next iteration of the
sequence.
Dostları ilə paylaş: