#!F-adobe-helvetica-medium-r-normal--18*
#!N
#!CNavyBlue #!N #!Rall269 Advanced Looping Constructs #!N #!EC #!N #!N
Combinations of the modules described above enable you to create advanced
looping constructs. These constructs are equivalent to C-language constructs such as
"do while" or "for" loops containing "break" and "continue" statements. In
the following figures the Sum and Increment macros, as described above,
are used as well as a macro named Equals that consists
of a Compute where the expression is "a==b?1:0" (if the inputs
are equal output 1 otherwise output 0). #!N #!N Illustrated in
#!Lxmodx844,dxall270 f Figure 44 #!EL is a macro that computes the sum of numbers from
1 to N. If a number in the sequence from 1
to N is equal to an external input, x, the loop
terminates and returns the sum from 1 to x. Done, in
combination with Equals, is used to cause early termination of the
loop. Done causes the loop to terminate after all the modules
in the macro have executed if the input to Done is
nonzero. The macro illustrated in #!Lxmodx844,dxall270 f Figure 44 #!EL is equivalent to the C-language
statements: #!CForestGreen #!N #!N #!F-adobe-courier-bold-r-normal--18* #!N sum = 0; #!N i
= 0; #!N do #!N { #!N i++; #!N sum =
sum+i; #!N } while (i<=n && i!=x); #!EF #!N #!N #!EC
#!N #!N Now consider a macro in which the sum of
numbers from 1 to N is computed, but if a number
is equal to an external input value, x, it is excluded
from the sum. To achieve this result using C-language statements, you
would use a conditional with a "continue" statement: #!CForestGreen #!N #!N
#!F-adobe-courier-bold-r-normal--18* #!N sum = 0; #!N for (i=1; i<=n; i++) #!N
{ #!N if (i==x) continue; #!N sum = sum+i; #!N }
#!EF #!N #!N #!EC #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx844 #!N Graphics omitted
from Online Documentation. Please see the manual. #!N #!N Figure 44.
Example 8 #!EF #!N #!EC As illustrated in #!Lxmodx945,dxall270 f Figure 45 #!EL , you
would use Route to create this macro using Data Explorer. The
#!F-adobe-times-bold-r-normal--18* selector #!EF input of Route is being controlled by the
output of Compute. The Compute has its expression set to "a==b?0:1"
(if a and b are equal output 0, otherwise output 1).
(This is similar to the Equal macro used earlier, but the
expression differs slightly.) Therefore, if the iteration variable is equal to
x, Compute outputs a 0, causing Route to disable the execution
of all the modules downstream from it. This implies that Sum
and SetLocal will not run; therefore, during the next iteration, GetLocal
will retrieve the same value as the current iteration. #!N #!N
Unfortunately, the visual program illustrated in #!Lxmodx945,dxall270 f Figure 45 #!EL has a minor problem.
If x equals N, the Route will cause the Sum and
SetLocal not to execute during the last iteration; therefore the output
of the macro will be a NULL. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx945
#!N Graphics omitted from Online Documentation. Please see the manual. #!N
#!N Figure 45. Example 9 #!EF #!N #!EC Illustrated in #!Lxmodx1046,dxall270 f Figure 46 #!EL
is the fix to the problem. A Switch is included to
choose the correct input for the output of the macro. If
x equals N, the output of the GetLocal is chosen; otherwise
the output of Sum is chosen. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx1046 #!N
Graphics omitted from Online Documentation. Please see the manual. #!N #!N
Figure 46. Example 10 #!EF #!N #!EC #!N #!N If you
want to create a loop containing an early exit in the
middle of the loop (a "break"), you need to use a
Route in combination with Done. Illustrated in #!Lxmodx1147,dxall270 f Figure 47 #!EL is a macro
that performs the equivalent function as the C-language statements: #!CForestGreen #!N
#!N #!F-adobe-courier-bold-r-normal--18* #!N sum = 0; #!N for (i=1; i<=n; i++)
#!N { #!N if (i==x) break; #!N sum = sum+i; #!N
} #!EF #!N #!N #!EC #!N #!N Data Explorer allows you
to have multiple Done tools in a single loop enabling you
to have more than one break or continue or combinations of
the two. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx1147 #!N #!N Graphics omitted from
Online Documentation. Please see the manual. #!N Figure 47. Example 11
#!EF #!N #!EC #!N #!N ForEachN or ForEachMember simplify the use
of loops but they are not necessary for creating them. In
fact, Done itself is sufficient, if it is included inside a
macro. The macro will execute repeatedly as long as the #!F-adobe-times-bold-r-normal--18*
done #!EF parameter is equal to 0 (zero). Note that the
top-level visual program is itself a macro, so the same behavior
will occur if Done is placed in the top-level visual program.
#!N #!N Illustrated in #!Lxmodx1248,dxall270 f Figure 48 #!EL is a macro that computes the
Fibonacci Series (defined by setting Y[1]= 1, Y[2] = 1 and
by the recursion formula Y[k] = Y[k-2] + Y[k-1], for k
= 3,4,5...). In this example a two vector, [Y[k-1], Y[k]], is
used to store the elements of the series. The GetLocal module
has its initial value set to [1,1]. The first Compute in
the macro creates a new two vector consisting of [Y[k-1], Y[k]]
using the expression "[a.1, a.0 + a.1]." The second Compute in
the macro extracts Y[k] from the two vector using the expression
"a.1." To terminate the loop, the Y[k] element of the series
is checked against an external input, x. If Y[k] is greater
than x, the loop terminates. GreaterThan is a simple macro consisting
of a Compute with its expression set to "a>b?1:0." An equivalent
set of C-language statements is: #!CForestGreen #!N #!N #!F-adobe-courier-bold-r-normal--18* #!N a=1;
#!N b=1; #!N do { #!N c = b; #!N b
= b + a; #!N a = c; #!N } while
(b <= x); #!EF #!N #!N #!EC #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx1248
#!N Graphics omitted from Online Documentation. Please see the manual. #!N
#!N Figure 48. Example 12 #!EF #!N #!EC #!N #!N #!N
#!F-adobe-times-medium-i-normal--18* Next Topic #!EF #!N #!N #!Lall270,dxall271 h External Asynchronous Data Sources #!EL #!N #!F-adobe-times-medium-i-normal--18* #!N