TOPS-20 PASCAL Language Manual - Bitsavers

PASCAL STATEMENTS
In the DOWNTO form,
than or equal to
control variable is
variable is less
complete.
if the value of the control variable is greater
the final value, the loop is executed, and the
decremented. When the value of the control
than the final value, execution of the loop is
Because completion tests are performed before the statement is
executed, some loops are never executed, for example:
FOR Control := N TO N + Q DO
Wpek r: N ] :::~ We (::)k [N] + Newpa~:I'
If the value of N + Q is less than the value of N (that is,
negative), the loop is never execut,ed.
if Q
is
When incrementing and decrementing the control variable, PASCAL uses
units of the appropriate type. For numeric values, it adds or
subtracts one upon each iteration. For values of other types, the
control variable takes on each successive value of the type. For
example, a control variable of type 'A' •. '2' is incremented (or
decremented) by one character each time the loop is executed.
If the FOR loop terminates normally, that is, if the loop exits upon
completion and not because of a GOTO statement, the value of the
control variable is left undefined. You cannot assume that it retains
a value. Therefore, you must assign a new value to the control
variable if you use it elsewhere in the program. However, if the FOR
loop terminates because of a GOTO statement, it retains the value it
had at termination; and you can use that value elsewhere.
Example I
FOR N := Lowbound TO HiShbound DO
Sum := Sum + IntArra~[NJ;
This FOR loop computes the sum of the elements of Int_luray with index
values from Lowbound through Highbound.
Example 2
FOR Year := 1899 DOWN TO 1801 DO
IF (Year MOD 4) = 0 THEN
WRITELN(Year:4,' IS A LEAP YEAR');
The DOWNTO form is used here to print a list of all the leap years
the nineteenth century.
in
Example 3
FOR I := 1 TO 10 DO
FOR J := 1 TO 10 DO
A[I,JJ := 0;
This example shows how you can directly nest FOR loops. For each
value of I, the system steps through all 10 values of J and assigns
the value 0 to the appropriate array element.
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