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Date: Wed, 11 Dec 1996 22:34:08 GMTServer: NCSA/1.5Content-type: text/htmlLast-modified: Fri, 18 Oct 1996 17:50:49 GMTContent-length: 7663<HTML><HEAD><TITLE>CS 302 Section 70 Lecture Notes - Week 7</TITLE></HEAD><BODY><H2><!WA0><!WA0><!WA0><A HREF="http://www.cs.wisc.edu/~tick/cs302.html#text" ><!WA1><!WA1><!WA1><IMG SRC="http://www.cs.wisc.edu/~bestor/icons/arrowleft.gif" WIDTH=15 HEIGHT=15></A> Lecture Notes - Week 7</H2><HR><DL> <DT>Topic: <DD>Multi-dimensional arrays. Multi-dimensional array arguments. Parallel arrays.<P> <DT>Text: <DD>8.1 - 8.3<P> <DT>Notes: <DD> <HR> <CENTER> <H3>Two-Dimensional Arrays</H3> </CENTER> <H4>One-Dimensional Arrays</H4> <UL> <LI>1-D arrays have <EM>one subscript</EM>. The subscript specifies which value in the array you want. <LISTING> INTEGER SCORES(10) ... PRINT *, SCORES(3) </LISTING> <LI>View the array as a single <EM>row</EM> of boxes. <LISTING> SCORES() 1 2 3 4 5 6 7 8 9 10 +---+---+---+---+---+---+---+---+---+---+ |-15|83 |92 |132|73 | 9 |27 |-54|82 |294| +---+---+---+---+---+---+---+---+---+---+ </LISTING> <LI>Only <STRONG>one</STRONG> subscript is needed to uniquely specify any particular position in the array. </UL> <H4>Two-Dimensional Arrays</H4> <UL> <LI>2-D arrays have <EM>two</EM> subscripts. <LISTING> arrayname(sizeX,sizeY) CHARACTER TICTAC(3,3) </LISTING> <LI>The size of the array (i.e. number of values it can store) equals <EM>sizeX*sizeY</EM> <LISTING> TICTAC(1,1), TICTAC(1,2), TICTAC(1,3), TICTAC(2,1), TICTAC(2,2), TICTAC(2,3), TICTAC(3,1), TICTAC(3,2), TICTAC(3,3), </LISTING> <TT>3*3 = 9</TT> different values! <LI>To access a particular value specify both its subscripts; i.e. the <EM>column</EM> (X coordinate) and <EM>row</EM> (Y coordinate). <LISTING> arrayname(column, row) PRINT *, TICTAC(3,2) READ *, TICTAC(X,Y) </LISTING> <LI><STRONG>Important</STRONG>: The order of the subscripts is <STRONG>very</STRONG> important. <LISTING> TICTAC(3,2) .NE. TICTAC(2,3) </LISTING> <LI>View a 2-D array as a <EM>grid</EM>. <LISTING> TICTAC(X,Y) +---+---+---+ 3 | O | X | X | +---+---+---+ Y = 2 | O | X | O | +---+---+---+ 1 | X | O | O | +---+---+---+ X = 1 2 3 </LISTING> <LI><STRONG>Two</STRONG> subscripts are needed to uniquely specify a position in the grid; i.e. the <EM>column</EM> and <EM>row</EM>. <LI>As with 1-D arrays, subscripts can be <EM>literals</EM>, <EM>variables</EM> or <EM>expressions</EM>, or any combination thereof. <LISTING> TICTAC(COL, 2) TICTAC(1,NINT(-COS(180)*2)) </LISTING> <LI>2-D arrays do not have to be <EM>square</EM>. The number of rows and columns can differ. <LISTING> INTEGER GRADES(10,4) ... PRINT *, 'Grades for student',STU DO GRA = 1,4 PRINT *, GRADES(STU,GRA) END DO </LISTING> </UL> <HR> <CENTER> <H3>2-D Arrays and DO Loops</H3> </CENTER> <UL> <LI>1-D arrays are processed with a single <TT>DO</TT> loops whose counter is used as the array subscript. <LISTING> DO COUNT = 1, MAXSIZ PRINT *, SCORES(COUNT) END DO </LISTING> <LI>2-D arrays are processed with <EM>two</EM> <TT>DO</TT> loops. Both counters are used as array subscripts. <STRONG>Important</STRONG>: <TT>DO</TT> loops must be <EM>nested</EM>. <LISTING> DO Y = 3, 1, -1 DO X 1, 3 PRINT *, TICTAC(X,Y) END DO END DO </LISTING> <LI>Use an <EM>implied DO loop</EM> for the <STRONG>inner</STRONG> loop so that all the values for each row appear on the same line. <LISTING> C Print rows (Y-axis) DO 100 Y = 3, 1, -1 C Print columns of each row (X-axis) PRINT *, (TICTAC(X,Y), X = 1, 3) END DO </LISTING> <LI><STRONG>Important</STRONG>: outer loop for <EM>rows</EM> Y, inner loop for <EM>columns</EM> X. </UL> <HR> <CENTER> <H3>2-D Array Arguments</H3> </CENTER> <UL> <LI>To pass 1-D arrays as arguments to a user-defined function/subroutine, pass the array <EM>name</EM> and the array <EM>size</EM>. <LISTING> PRINT *, GETMAX(SCORES, MAXSIZ) ... INTEGER FUNCTION GETMAX (LIST, SIZE) </LISTING> <LI>To pass 2-D arrays as arguments, pass the array <EM>name</EM> and <STRONG>both</STRONG> the array sizes <EM>sizeX</EM> and <EM>sizeY</EM>. <LISTING> SHOW(TICTAC, 3, 3) ... SUBROUTINE SHOW(BOARD, SIZEX, SIZEY) C Prints the board on the screen C Declare arguments INTEGER SIZEX, SIZEY CHARACTER BOARD(SIZEX, SIZEY) C Print rows (Y-axis) DO Y = SIZEY, 1, -1 Print columns of each row (X-axis) PRINT *, (BOARD(X,Y), X = 1, SIZEX) END DO RETURN END </LISTING> </UL> <HR> <CENTER> <H3>DATA Statement</H3> </CENTER> <UL> <LI>The <TT>DATA</TT> statement provides a convenient way to initialize an array. <LISTING> DATA arrayname / value1, value2, ... / INTEGER MAXSIZ PARAMETER (MAXSIZ=8) INTEGER SCORES(MAXSIZ) DATA SCORES /83,94,75,39,97,86,91,73/ </LISTING> <LI><TT>DATA</TT> statement should appear <EM>immediately</EM> after the array declaration. <LI>Can initialize an array to all the same values, e.g. zero. <LISTING> DATA arrayname / arraysize * value/ DATA SCORES /MAXSIZ * 0/ </LISTING> </UL> <H4>Column-Major Order</H4> <UL> <LI>Internally, 2-D arrays are stored as a list of values (e.g. like a long 1-D array) in <EM>column-major order</EM> where each "column" is stored next to each other. In this case, the "column" is considered to be the first subscript; i.e. <TT>TICTAC(column, row)</TT> <LISTING> CHARACTER TICTAC(3,3) TICTAC(1,1), TICTAC(2,1), TICTAC(3,1), TICTAC(1,2), ... </LISTING> <LI>If <TT>PRINT</TT>, <TT>READ</TT> or <TT>WRITE</TT>the whole array, or initialize it with a <TT>DATA</TT> statement, then array values will be listed in column-major order. <LISTING> TICTAC(X,Y) +---+---+---+ 3 | O | X | X | +---+---+---+ Y= 2 | O | X | O | +---+---+---+ 1 | X | O | O | +---+---+---+ X = 1 2 3 </LISTING> For example, <LISTING> PRINT *, TICTAC </LISTING> prints <LISTING> X O O O X O O X X </LISTING> </UL> <HR> <CENTER> <H3>Parallel Arrays</H3> </CENTER> <UL> <LI>Often have several arrays of the same size storing related values. For example, a student's name, grades, year and GPA. <LISTING> INTEGER NUMSTU PARAMETER (NUMSTU = 50) CHARACTER *20 NAME(NUMSTU) INTEGER GRADES(NUMSTU,4) CHARACTER *2 YEAR(NUMSTU) REAL GPA(NUMSTU) </LISTING> <LI>Called <EM>parallel arrays</EM> because all the values for a particular student have the <EM>same</EM> subscript.<P> e.g. For student #7: <UL> <LI>Name = <TT>NAME(7)</TT> <LI>Grades = <TT>GRADES(7,X)</TT> [X=1..4] <LI>Year = <TT>YEAR(7)</TT> <LI>GPA = <TT>GPA(7)</TT> </UL> <LISTING> C Display every student's data DO S = 1, NUMSTU PRINT *, 'Name:', NAME(S) PRINT *, 'Grades:',(GRADES(S,X),X=1,4) PRINT *, 'Year:', YEAR(S) PRINT *, 'GPA:', GPA(S) END DO </LISTING> </UL></DL></BODY><HR><ADDRESS><H5>Copyright © 1996 Modified from<!WA2><!WA2><!WA2><A HREF="http://www.cs.wisc.edu/~bestor/bestor.html">Gareth S. Bestor</A> (<!WA3><!WA3><!WA3><A HREF="mailto:bestor@cs.wisc.edu">bestor@cs.wisc.edu</A>). Last modified October 18, 1996.</H5></ADDRESS> ⌨️ 快捷键说明
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