00001 #include "MusimatChapter9.h" 00002 MusimatChapter9Section(C091201a) { 00003 Print("*** Cycle ***"); 00004 /***************************************************************************** 00005 00006 Cycle 00007 00008 This method iterates a sequence either forward or backward. It can either select successive 00009 elements or skip through the list. When it reaches the end of the list (either end), it starts over at 00010 the other end. Its inputs are 00011 00012 o The list to traverse 00013 00014 o The previous position in the list 00015 00016 o Whether to move forward (prime) or backward (retrograde) 00017 00018 Its output is the next element in sequence based on its previous position in the list. As a side 00019 effect, it updates its position in the list. 00020 00021 If it traverses the list forward, it returns to the head of the list when it goes past the tail. If it 00022 traverses the list in retrograde, it returns to the tail of the list when it goes past the head. 00023 00024 In the following code example, setting inc to 1 moves forward one element every time 00025 cycle() is called, and setting inc to -1 moves backward one element at a time. Setting inc to 00026 any other value skips through the list by that amount, wrapping around at the ends. 00027 *****************************************************************************/ 00028 para1(); // Step into this function to continue. 00029 } 00030 00031 Integer cycle(IntegerList L, Integer Reference pos, Integer inc) { 00032 Integer i = PosMod(pos, Length(L)); // compute current index 00033 pos = PosMod(pos + inc, Length(L)); // compute index for next time 00034 Return(L[i]); 00035 } 00036 00037 Static Void para1() { 00038 /***************************************************************************** 00039 The pos argument keeps track of the position in the list. We wish to delegate to cycle() the 00040 job of managing the list position, so we declare pos as a Reference argument. Thus, when 00041 cycle() updates pos, the corresponding actual argument is changed. (If pos were not a 00042 Reference variable, any changes cycle() made to its value would be lost when it returns (see 00043 appendix B, B.1.22). 00044 00045 Here's an example of invoking cycle(): 00046 *****************************************************************************/ 00047 00048 Print("*** Cycling a list ***"); 00049 IntegerList L(10, 11, 12); 00050 Integer myPos = 0; 00051 Integer n = 2 * Length(L) -1; // go 1 less than two times through list 00052 00053 For (Integer i = 0; i < n; i = i + 1) 00054 Print(cycle(L, myPos, 1)); // 1 = forward direction 00055 00056 Print("myPos=", myPos); 00057 00058 /***************************************************************************** 00059 This program prints 10, 11, 12, 10, 11. Last, it prints myPos=2, proving that cycle() is 00060 changing the myPos parameter. 00061 *****************************************************************************/ 00062 } 00063 00065 /* $Revision: 1.3 $ $Date: 2006/09/05 08:02:45 $ $Author: dgl $ $Name: $ $Id: C091201a.cpp,v 1.3 2006/09/05 08:02:45 dgl Exp $ */ 00066 // The Musimat Tutorial © 2006 Gareth Loy 00067 // Derived from Chapter 9 and Appendix B of "Musimathics Vol. 1" © 2006 Gareth Loy 00068 // and published exclusively by The MIT Press. 00069 // This program is released WITHOUT ANY WARRANTY; without even the implied 00070 // warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 00071 // For information on usage and redistribution, and for a DISCLAIMER OF ALL 00072 // WARRANTIES, see the file, "LICENSE.txt," in this distribution. 00073 // "Musimathics" is available here: http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10916 00074 // Gareth Loy's Musimathics website: http://www.musimathics.com/ 00075 // The Musimat website: http://www.musimat.com/ 00076 // This program is released under the terms of the GNU General Public License 00077 // available here: http://www.gnu.org/licenses/gpl.txt 00078
1.7.2