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1 #!F-adobe-helvetica-medium-r-normal--18* 2 #!N 3 #!CNavyBlue #!N #!Rall269 Advanced Looping Constructs #!N #!EC #!N #!N 4 Combinations of the modules described above enable you to create advanced 5 looping constructs. These constructs are equivalent to C-language constructs such as 6 "do while" or "for" loops containing "break" and "continue" statements. In 7 the following figures the Sum and Increment macros, as described above, 8 are used as well as a macro named Equals that consists 9 of a Compute where the expression is "a==b?1:0" (if the inputs 10 are equal output 1 otherwise output 0). #!N #!N Illustrated in 11 #!Lxmodx844,dxall270 f Figure 44 #!EL is a macro that computes the sum of numbers from 12 1 to N. If a number in the sequence from 1 13 to N is equal to an external input, x, the loop 14 terminates and returns the sum from 1 to x. Done, in 15 combination with Equals, is used to cause early termination of the 16 loop. Done causes the loop to terminate after all the modules 17 in the macro have executed if the input to Done is 18 nonzero. The macro illustrated in #!Lxmodx844,dxall270 f Figure 44 #!EL is equivalent to the C-language 19 statements: #!CForestGreen #!N #!N #!F-adobe-courier-bold-r-normal--18* #!N sum = 0; #!N i 20 = 0; #!N do #!N { #!N i++; #!N sum = 21 sum+i; #!N } while (i<=n && i!=x); #!EF #!N #!N #!EC 22 #!N #!N Now consider a macro in which the sum of 23 numbers from 1 to N is computed, but if a number 24 is equal to an external input value, x, it is excluded 25 from the sum. To achieve this result using C-language statements, you 26 would use a conditional with a "continue" statement: #!CForestGreen #!N #!N 27 #!F-adobe-courier-bold-r-normal--18* #!N sum = 0; #!N for (i=1; i<=n; i++) #!N 28 { #!N if (i==x) continue; #!N sum = sum+i; #!N } 29 #!EF #!N #!N #!EC #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx844 #!N Graphics omitted 30 from Online Documentation. Please see the manual. #!N #!N Figure 44. 31 Example 8 #!EF #!N #!EC As illustrated in #!Lxmodx945,dxall270 f Figure 45 #!EL , you 32 would use Route to create this macro using Data Explorer. The 33 #!F-adobe-times-bold-r-normal--18* selector #!EF input of Route is being controlled by the 34 output of Compute. The Compute has its expression set to "a==b?0:1" 35 (if a and b are equal output 0, otherwise output 1). 36 (This is similar to the Equal macro used earlier, but the 37 expression differs slightly.) Therefore, if the iteration variable is equal to 38 x, Compute outputs a 0, causing Route to disable the execution 39 of all the modules downstream from it. This implies that Sum 40 and SetLocal will not run; therefore, during the next iteration, GetLocal 41 will retrieve the same value as the current iteration. #!N #!N 42 Unfortunately, the visual program illustrated in #!Lxmodx945,dxall270 f Figure 45 #!EL has a minor problem. 43 If x equals N, the Route will cause the Sum and 44 SetLocal not to execute during the last iteration; therefore the output 45 of the macro will be a NULL. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx945 46 #!N Graphics omitted from Online Documentation. Please see the manual. #!N 47 #!N Figure 45. Example 9 #!EF #!N #!EC Illustrated in #!Lxmodx1046,dxall270 f Figure 46 #!EL 48 is the fix to the problem. A Switch is included to 49 choose the correct input for the output of the macro. If 50 x equals N, the output of the GetLocal is chosen; otherwise 51 the output of Sum is chosen. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx1046 #!N 52 Graphics omitted from Online Documentation. Please see the manual. #!N #!N 53 Figure 46. Example 10 #!EF #!N #!EC #!N #!N If you 54 want to create a loop containing an early exit in the 55 middle of the loop (a "break"), you need to use a 56 Route in combination with Done. Illustrated in #!Lxmodx1147,dxall270 f Figure 47 #!EL is a macro 57 that performs the equivalent function as the C-language statements: #!CForestGreen #!N 58 #!N #!F-adobe-courier-bold-r-normal--18* #!N sum = 0; #!N for (i=1; i<=n; i++) 59 #!N { #!N if (i==x) break; #!N sum = sum+i; #!N 60 } #!EF #!N #!N #!EC #!N #!N Data Explorer allows you 61 to have multiple Done tools in a single loop enabling you 62 to have more than one break or continue or combinations of 63 the two. #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx1147 #!N #!N Graphics omitted from 64 Online Documentation. Please see the manual. #!N Figure 47. Example 11 65 #!EF #!N #!EC #!N #!N ForEachN or ForEachMember simplify the use 66 of loops but they are not necessary for creating them. In 67 fact, Done itself is sufficient, if it is included inside a 68 macro. The macro will execute repeatedly as long as the #!F-adobe-times-bold-r-normal--18* 69 done #!EF parameter is equal to 0 (zero). Note that the 70 top-level visual program is itself a macro, so the same behavior 71 will occur if Done is placed in the top-level visual program. 72 #!N #!N Illustrated in #!Lxmodx1248,dxall270 f Figure 48 #!EL is a macro that computes the 73 Fibonacci Series (defined by setting Y[1]= 1, Y[2] = 1 and 74 by the recursion formula Y[k] = Y[k-2] + Y[k-1], for k 75 = 3,4,5...). In this example a two vector, [Y[k-1], Y[k]], is 76 used to store the elements of the series. The GetLocal module 77 has its initial value set to [1,1]. The first Compute in 78 the macro creates a new two vector consisting of [Y[k-1], Y[k]] 79 using the expression "[a.1, a.0 + a.1]." The second Compute in 80 the macro extracts Y[k] from the two vector using the expression 81 "a.1." To terminate the loop, the Y[k] element of the series 82 is checked against an external input, x. If Y[k] is greater 83 than x, the loop terminates. GreaterThan is a simple macro consisting 84 of a Compute with its expression set to "a>b?1:0." An equivalent 85 set of C-language statements is: #!CForestGreen #!N #!N #!F-adobe-courier-bold-r-normal--18* #!N a=1; 86 #!N b=1; #!N do { #!N c = b; #!N b 87 = b + a; #!N a = c; #!N } while 88 (b <= x); #!EF #!N #!N #!EC #!Cbrown #!N #!F-adobe-times-medium-r-normal--18* #!Rxmodx1248 89 #!N Graphics omitted from Online Documentation. Please see the manual. #!N 90 #!N Figure 48. Example 12 #!EF #!N #!EC #!N #!N #!N 91 #!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