Operator Reference
for (Operator)
for — Starts a loop block that is usually executed for a fixed number of
iterations.
Signature
Description
Syntax in HDevelop: for Index := Start to End by Step
The for statement starts a loop block that is usually executed
for a fixed number of iterations.
The for block ends at the corresponding endfor statement.
The number of iterations is defined by the Start value, the
End value, and the increment value Step.
All of these parameters can be initialized with expressions or variables
instead of constant values.
Please note that these loop parameters are evaluated only once, namely,
immediately before the for loop is entered.
They are not re-evaluated after the loop cycles, i.e., any modifications of
these variables within the loop body will have no influence on the number
of iterations.
The passed loop parameters must be either of type integer or
real.
If all input parameters are of type integer, the Index
variable will also be of type integer.
In all other cases the Index variable will be of type real.
At the beginning of each iteration the loop variable Index is
compared to the End parameter.
If the increment value Step is positive, the for loop
is executed as long as the Index variable is less than or
equal to the End parameter.
If the increment value Step is negative, the for loop
is executed as long as the Index variable is greater than or
equal to the End parameter.
Attention: If the increment value Step is set to a
value of type real, it may happen that the last loop cycle is
omitted owing to rounding errors in case the Index variable is
expected to match the End value exactly in the last cycle.
Hence, on some systems the following loop is not executed---as
expected---for four times (with the Index variable set to 1.3,
1.4, 1.5, and 1.6), but only three times because after three additions the
index variable is slightly greater than 1.6 due to rounding errors.
I:=[]
for Index := 1.3 to 1.6 by 0.1
I := [I,Index]
endfor
endfor statement or a continue statement,
the increment value (as initialized at the beginning of the for
loop) is added to the current value of the loop counter Index.
Then, the loop condition is re-evaluated as described above.
Depending on the result the loop is either executed again or finished
in which case execution continues with the first statement after the
corresponding endfor statement.
A break statement within the loop---that is not covered by
a more internal block---leaves the loop immediately and execution continues
after the corresponding endfor statement.
In contrast, the continue statement is used to ignore the rest of
the loop body in the current cycle and continue execution with adapting the
Index variable and re-evaluating the loop condition.
Attention: It is recommended to avoid modifying the
Index variable of the for loop within its body.
If the for loop is stopped, e.g., by a stop statement or by
pressing the Stop button, and if the PC is placed manually by the
user, the for loop is continued at the current iteration as long as
the PC remains within the for body or is set to the endfor
statement.
If the PC is set on the for statement (or before it) and executed
again, the loop is reinitialized and restarts at the beginning.
Parameters
Start (input_control) number → (integer / real)
Start value of the loop variable.
Default: 1
End (input_control) number → (integer / real)
End value of the loop variable.
Default: 5
Step (input_control) number → (integer / real)
Increment value of the loop variable.
Default: 1
Index (output_control) number → (integer / real)
Loop variable.
Example (HDevelop)
read_image (Image, 'fabrik')
threshold (Image, Region, 128, 255)
connection (Region, ConnectedRegions)
select_shape (ConnectedRegions, SelectedRegions, 'area', 'and', 150, 99999)
area_center (SelectedRegions, Area, Row, Column)
dev_close_window ()
dev_open_window (0, 0, 512, 512, 'black', WindowHandle)
dev_display (Image)
dev_display (SelectedRegions)
dev_set_color ('white')
for Index := 0 to |Area| - 1 by 1
set_tposition (WindowHandle, Row[Index], Column[Index])
write_string (WindowHandle, 'Area=' + Area[Index])
endfor
Result
If the values of the specified parameters are correct,
for (as an operator) returns 2 (
H_MSG_TRUE)
. Otherwise, an
exception is raised and an error code is returned.
Alternatives
See also
repeat,
break,
continue,
endfor
Module
Foundation