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Date: Wed, 11 Dec 1996 22:34:16 GMTServer: NCSA/1.5Content-type: text/htmlLast-modified: Sun, 06 Oct 1996 22:35:37 GMTContent-length: 13997<HTML><HEAD><TITLE>CS 302 Section 70 Lecture Notes - Weeks 5</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/~tick/icons/arrowleft.gif" WIDTH=15 HEIGHT=15></A> Lecture Notes - Week 5</H2><HR><DL> <DT>Topic: <DD>Formatted input and output. Reading and writing files.<P> <DT>Text: <DD>Chp. 5.1, 5.3, 5.5 - 5.7<P> <DT>Notes: <DD> <HR> <CENTER> <H3>Formatted Output</H3> </CENTER> <UL> <LI>So for we have been using <EM>unformatted</EM> output. <LISTING> PRINT *, 'Total = ', TOT </LISTING> prints <LISTING> Total = 12345 </LISTING> with extraneous spaces in front of the number. <LI>The <TT>*</TT> specifies to use the default output format to print the items on the line. <LI>Alternatively, replace the <TT>*</TT> with the label of a <TT>FORMAT</TT> statement which describes how to print the items. <LISTING> PRINT 15, 'Total = ', TOT 15 FORMAT(1X, A, I5) </LISTING> prints <LISTING> Total = 12345 </LISTING> <LI>The <TT>FORMAT</TT> statement should immediately follow the <TT>PRINT</TT> statement. <LI>The items in the <TT>FORMAT</TT> statement are called <EM>edit descriptors</EM> and describe the appearance of the line. <LI>Each item in the <TT>PRINT</TT> statement has a corresponding edit descriptor in the <TT>FORMAT</TT> statement specifying how to print it. </UL> <H4>Edit Descriptors</H4> <UL> <LI>The first item in the <TT>FORMAT</TT> statement describes the <EM>line spacing</EM>. The most common is <EM>single spacing</EM> specified by <TT>1X</TT>. <LISTING> 15 FORMAT(1X, .... ) </LISTING> <LI>The edit descriptor depends on the <EM>type</EM> of the value being printed. <UL> <LI><TT>Iw</TT> - <TT>INTEGER</TT> <LI><TT>Fw.d</TT> - <TT>REAL</TT> <LI><TT>Aw</TT> - <TT>CHARACTER</TT> (i.e. strings) <LI><TT>nX</TT> - insert spaces between items </UL> </UL> <H4>INTEGER - Iw</H4> <UL> <LI><TT>INTEGER</TT>s are printed <EM>right-justified</EM> in <TT>w</TT> columns. <LI>If the <TT>INTEGER</TT> is shorter than <TT>w</TT> columns wide then it is printed with leading blanks (indicated by a #). <LISTING> TOT = 87 PRINT 15, 'Total=',TOT,'cents' 15 FORMAT(1X, A, I4, A) </LISTING>prints <LISTING> Total=##87cents ^^^^ </LISTING> <LI>Negative <TT>INTEGER</TT>s are printed with a leading minus "-" sign. <LI>If the <TT>INTEGER</TT> is longer than <TT>w</TT> columns wide (i.e. it doesn't fit in the width specified) then "*"s are printed instead. <LISTING> TOT = 12345 PRINT 15, TOT 15 FORMAT(1X, I4) </LISTING> prints <LISTING> **** </LISTING> </UL> <H4>REAL - Fw.d</H4> <UL> <LI><TT>REAL</TT>s are printed <EM>right-justified</EM> in <TT>w</TT> columns and <EM>rounded</EM> to <TT>d</TT> decimal places. <LISTING> MASS = -87.4395 PRINT 15, MASS 15 FORMAT(1X, F8.2) </LISTING> prints <LISTING> ##-87.44 ^^^^^^^^ </LISTING> <LI>Be sure to allow space for the sign (if negative) and decimal place, both of which take up an additional column each. </UL> <H4>CHARACTER - Aw</H4> <UL> <LI><TT>CHARACTER</TT> strings are printed <EM>right-justified</EM> in <TT>w</TT> columns. <LI>If the string is shorter than <TT>w</TT> columns then it is printed with leading blanks (indicated by a #). <LISTING> CHARACTER *11 NAME NAME = 'Christopher' PRINT 15, NAME 15 FORMAT(1X, A15) </LISTING> prints <LISTING> ####Christopher </LISTING> <LI>If the string is longer than <TT>w</TT> columns then it is <EM>left-justified</EM> and the characters at the end are truncated. <LISTING> PRINT 15, NAME 15 FORMAT(1X, A8) </LISTING> prints <LISTING> Christop </LISTING> <LI>Use <TT>A</TT> with no width specified to print the string in the same number of columns as its declared length. <LISTING> PRINT 15, NAME 15 FORMAT(1X, A) (same as A11) </LISTING> </UL> <H4>Insert Spaces - nX</H4> <UL> <LI>Spaces/blanks can be inserted between any two items in the <TT>PRINT</TT> statement. <LISTING> PRINT 15,'Hello','there','world' 15 FORMAT(1X, A, 2X, A, 3X, A) </LISTING> prints <LISTING> Hello##there###world ^^ ^^^ </LISTING> </UL> <H4>PRINT Statement</H4> <UL> <LI>The edit specifiers can be inserted directly into the <TT>PRINT</TT> statement without using a separate <TT>FORMAT</TT> statement and label. <LISTING> NAME = 'Christopher' PRINT '(1X, A15)', NAME </LISTING> <LI>The edit descriptors are enclosed in brackets and apostrophes. </UL> <HR> <CENTER> <H3>Formatted Input</H3> </CENTER> <UL> <LI>Unformatted input: <OL> <LI>All the data on the line has to be read into variables. <LI>Multiple values on the same line must be separated by spaces. <LI>Strings must be entered enclosed in apostrophes. </OL> <LI>If the format of the input data does not match these requirements then <EM>formatted</EM> input must be used instead. <LI>Example: multiple values separated by a <EM>hyphen</EM>. <LISTING> Please enter today's date: 10-08-95 </LISTING> <LI><STRONG>IMPORTANT</STRONG> - Formatted input specifies which columns are read in and which are skipped. <LI>Use a <TT>FORMAT</TT> statement with edit descriptors to specify the type and width of each value to read in. <LISTING> READ 15, MONTH, DAY, YEAR 15 FORMAT(I2, 1X, I2, 1X, I2) </LISTING> <LI>Note: no line spacing is specified for formatted <EM>input</EM>. </UL> <H4>Edit Descriptors</H4> <UL> <LI>Same descriptors as formatted output. <UL> <LI><TT>Iw</TT> - <TT>INTEGER</TT> <LI><TT>Fw.d</TT> - <TT>REAL</TT> <LI><TT>Aw</TT> - <TT>CHARACTER</TT> (i.e. strings) <LI><TT>nX</TT> - skip characters between values </UL> </UL> <H4>INTEGER - Iw</H4> <UL> <LI>Read only the next <TT>w</TT> digits as an <TT>INTEGER</TT> value. <LISTING> READ 15, NUM 15 FORMAT(I3) </LISTING> User enters <LISTING> 12345 (NUM = 123) ^^^ </LISTING> User enters <LISTING> -12345 (NUM = -12) ^^^ </LISTING> <LI>Only <TT>w</TT> digits are read. Any additional digits are <EM>ignored</EM>. </UL> <H4>REAL - Fw.d</H4> <UL> <LI>Read only the next <TT>w</TT> digits as an <TT>REAL</TT> value, where the last <TT>d</TT> digits are to the right of the decimal point. <LISTING> READ 15, PRICE 15 FORMAT(F6.2) </LISTING> User enters <LISTING> 123.4567 (PRICE = 123.45) ^^^^^^ </LISTING> <LI><STRONG>WARNING</STRONG>: The decimal place is optional. If missing, the computer uses <TT>d</TT> to determine where it <EM>should</EM> have been. User enters <LISTING> 1234567 (PRICE = 1234.56 !) ^^^^^^ </LISTING> <LI>If the user does enter a decimal point then it over-rides the value of <TT>d</TT>. User enters <LISTING> 12.34567 (PRICE = 12.345) ^^^^^^ </LISTING> <LI>Only <TT>d</TT> digits are read. Any additional digits are <EM>ignored</EM>. </UL> <H4>CHARACTER - Aw</H4> <UL> <LI>Read the next <TT>w</TT> letters as a <TT>CHARACTER</TT> string and store them <EM>exactly</EM> as entered. <LISTING> CHARACTER *10 NAME READ 15, NAME 15 FORMAT(A7) </LISTING> User enters <LISTING> Kilroy1994junior (NAME='Kilroy1###') ^^^^^^^ </LISTING> <LI>If <TT>w</TT> is not specified then read in the same number of characters as the declared length of the variable. <LISTING> READ 15, NAME 15 FORMAT(A) </LISTING> User enters <LISTING> Kilroy1994junior (NAME='Kilroy1994') ^^^^^^^^^^ </LISTING> <LI>Note: The string is <STRONG>not</STRONG> enclosed by apostrophes! <LISTING> READ '(A)', NAME </LISTING> User enters <LISTING> Kilroy (NAME='Kilroy#####') </LISTING> </UL> <H4>Skip Characters - nX</H4> <UL> <LI>Skip over <TT>n</TT> characters in the input (e.g. a comma or hyphen). <LISTING> CHARACTER *10 NAME READ 15, NAME, YEAR, FEES 15 FORMAT(A, 1X, I4, 3X, F6.2) </LISTING> User enters <LISTING> Kilroy,Joe,1997###1368.25 ^^^^^^^^^^^^^^^^^^^^^^^^ NAME = 'Kilroy,Joe' YEAR = 1997 FEES = 1368.2 </LISTING> </UL> <HR> <CENTER> <H3>Reading and Writing Files</H3> </CENTER> <UL> <LI><EM>Interactive processing</EM> reads data from the keyboard and prints the results to the screen. <LI><EM>Batch processing</EM> reads data directly from a file on disk and stores the results in another file on disk. </UL> <H4>OPEN Statement</H4> <UL> <LI>Before you can read or write to a file it must be <EM>opened</EM>. <LI>The <TT>OPEN</TT> statement specifies the <EM>name</EM> of the file, assigns it a <EM>unit nummber</EM> and specifies whether the file will be <EM>read</EM> from or <EM>written</EM> to. <LISTING> OPEN(UNIT=1, FILE='MYDATA', STATUS='OLD') OPEN(UNIT=2, FILE='RESULTS', STATUS='NEW') </LISTING> <LI>To read from a file <TT>STATUS</TT> is 'OLD'. <LI>To write to a file <TT>STATUS</TT> is 'NEW'. <LI>Any unique number can be used for the <TT>UNIT</TT> number, except 5 and 6 which are reserved for the keyboard and screen. </UL> <H4>Reading From Files</H4> <UL> <LI>Use a modified <TT>READ</TT> statement to read from a file rather than the keyboard. Note: no comma before the list of variables. <LISTING> READ (unit-number, *) variables READ (1, *) X, Y, Z </LISTING> <LI>Must <TT>OPEN</TT> the file before you can read from it. <LI>Can also read formatted data from files. <LISTING> READ (1, 15) X, Y, Z 15 FORMAT (3F6.2) </LISTING> <LI>If the line contains more data than is read in then the rest of the line is ignored. e.g. <LISTING> 131.92-21.67 18.412345 ^^^^^^^^^^^^^^^^^^----- </LISTING> <LI>If the line contains less data than is read in the the <EM>next</EM> line is also read in. e.g. <LISTING> 131.92-21.67 ^^^^^^^^^^^^ 18.412345 ^^^^^^--- </LISTING> </UL> <H4>Writing To Files</H4> <UL> <LI>Use the <TT>WRITE</TT> statement to write to a file rather than the screen. Note: no comma before list of items. <LISTING> WRITE (unit-number, *) items WRITE (2, *) 'The answer is', 42 </LISTING> <LI>Must <TT>OPEN</TT> the file before you write to it. <LI>Can also write formatted data to files. <LISTING> WRITE (2, 15) X, Y, Z 15 FORMAT (3F6.2) </LISTING> </UL> <H4>Batch Processing</H4> <UL> <LI>Can read/write <EM>several</EM> files at the same time. Each file must have a unique unit number. <LISTING> OPEN(UNIT=1, FILE='DATA1', STATUS='OLD') OPEN(UNIT=2, FILE='DATA2', STATUS='OLD') OPEN(UNIT=3, FILE='RESULT', STATUS='NEW') READ (1,*) NUM1 READ (2,*) NUM2 WRITE (3, *) NUM1 + NUM2 </LISTING> <LI>Can still read from the keyboard and write to the screen at the same time. <LISTING> READ (1,*) NUM1 PRINT *, 'Please enter a number' READ *, NUM2 WRITE (3, *) NUM1 + NUM2 </LISTING> <LI>If you are reading from a file you don't need prompts (redundant). </UL> <H4>End-of-File (writing)</H4> <UL> <LI>When you have finished writing everything to an output file, write a special <EM>end-of-file</EM> marker at the end. <LISTING> END FILE (UNIT=3) </LISTING> <LI>Must be the last thing written to the file. </UL> <H4>CLOSE Statement</H4> <UL> <LI>When you have finished using either an input or an output file then <TT>CLOSE</TT> it. <LISTING> READ (1, *) NUM1 READ (2, *) NUM2 WRITE (3, *) NUM1 + NUM2 END FILE (UNIT=3) CLOSE (UNIT=1) CLOSE (UNIT=2) CLOSE (UNIT=3) </LISTING> <LI>Usually these are last few statements in your program before the <TT>STOP</TT> and <TT>END</TT>. </UL> <H4>End-of-File (reading)</H4> <UL> <LI>Unlike the keyboard where the user can always keep typing, eventually all the data in a file will be read in. <LI>When there's no more data to be read, the computer will reach the <EM>end-of-file marker</EM>. Generally you want to do something special when this happens; for example, exit a loop. <LI>A modified <TT>READ</TT> statement jumps to a <TT>CONTINUE</TT> statement when it reaches the end-of-file marker. <LISTING> OPEN(UNIT=1, FILE='DATA', STATUS='OLD') SUM = 0 C Add up all the numbers in the file DO WHILE (.TRUE.) READ (1, *, END=20) NUM SUM = SUM + NUM END DO C Reached the end-of-file so print the sum 20 CONTINUE PRINT *, SUM CLOSE (UNIT=1) STOP END </LISTING> <LI>Normally the <TT>CONTINUE</TT> is the first statement after the end of a <TT>DO/END DO</TT> loop. <LI>Similar to a <TT>GOTO</TT> statement to exit the loop. <LI>Exits the loop when the <TT>READ</TT> statement is re-executed and there's no more data to read; i.e. <STRONG>not</STRONG> immediately after the last number is read. </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 6, 1996.</H5></ADDRESS></HTML>⌨️ 快捷键说明
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