COSC 1P02 Introduction to Computer Science 8.1 Cosc 1P02 “For myself, I am an optimist--it does not seem to be much use being anything else.” Winston Churchill

COSC 1P02 Introduction to Computer Science 8.2 Class Average  Marks for test in a course  Average is sum divided by number of marks  Running total  sum values as see them  at each point sum is sum of values so far  add next value  initial value (no values so far) is 0  Summation algorithm  Reading data  ASCIIPrompter  Writing results  ASCIDisplayer  Example

ASCIIPrompter Methods

ASCIIDisplayer Methods

COSC 1P02 Introduction to Computer Science 8.6 Reading Data from a File  Tedious and error prone to enter data as program running  Instead create a file of data (text editor/word processor)  Reading data from a file  ASCIIDataFile  fields (tab delimited)  Example  data includes student number  not really a number but text  String  report  header, body (detail lines), summary  separate methods for each part

ASCIIDataFile Methods

COSC 1P02 Introduction to Computer Science 8.8 End of File  Tedious and error prone for user to have to count number of pieces of data  A file contains a finite amount of data  each read consumes one value  eventually a read must happen when there is no more data  called End Of File (EOF)  method isEOF() returns true when last read failed because of EOF  Indefinite loop  need to loop an unknown number of times  loop until something happens  Example  expect if student number then will be mark  count number of students

COSC 1P02 Introduction to Computer Science 8.10 while Statement  An indefinite loop  Syntax  Execution  evaluates condition  if true, executes body  if false, quits (continues after body)  Read to end of file loop  condition always true so executes body  if statement  if condition is true, executes then part  then part is one statement so doesn’t need {}  break statement quits whatever loop it is executed within

COSC 1P02 Introduction to Computer Science 8.13 Fill a Box  Problem  packing to move  Condition  Termination  infinite loop  Generating random values  Math.random()  Output  Summation

COSC 1P02 Introduction to Computer Science 8.14 While...

COSC 1P02 Introduction to Computer Science 8.15 Filling a Box

COSC 1P02 Introduction to Computer Science 8.16 Fill private void fill ( ) { intsize;// capacity of box intamt;// amount in box intitem;// item item to pack in.setLabel("Enter box size"); size = in.readInt(); writeSize(size); amt = 0; while ( amt < size ) { item = (int) (10 * Math.random() + 1); amt = amt + item; writeItem(item,amt); }; writeResult(amt); };// fill Condition checks if the amount put into the box exceeds the capacity. While this condition is true the “while loop” keeps repeating. We put an item into the box of varying size. Calculated using random(). Keep a running total of what is in the box.

COSC 1P02 Introduction to Computer Science 8.17 High and Low Mark  Algorithm  is value higher (lower) the highest (lowest) so far  Initial state?  Double.MAX_VALUE  Independent if s  independent decisions  Finding maximum value pattern

COSC 1P02 Introduction to Computer Science 8.18

COSC 1P02 Introduction to Computer Science 8.19 Finding the Maximum (minimum) Value Programming Pattern

COSC 1P02 Introduction to Computer Science 8.20 private void display ( ) { intnumStd;// number of students doubletotMark;// total of marks doubleaveMark;// average mark doublehighMark;// highest mark doublelowMark;// lowest mark intaStdNum;// one student's student nmber doubleaMark;// one student's mark numStd = 0; totMark = 0; highMark = - Double.MAX_VALUE; lowMark = Double.MAX_VALUE; while ( true ) { aStdNum = in.readInt(); if (in.isEOF() ) break; aMark = in.readDouble(); numStd = numStd + 1; totMark = totMark + aMark; if ( aMark > highMark ) { highMark = aMark; }; if ( aMark < lowMark ) { lowMark = aMark; }; aveMark = totMark / numStd; writeDetail(numStd,aveMark,highMark,lowMark); };// display High Mark.. Initialization of the hi and lo mark. If the new mark is higher then the previous high mark then replace with new mark. The same is done for the low mark, inequality is changed

COSC 1P02 Introduction to Computer Science 8.21 Reports  Most data processing involves production of a report (typically printed)  Report  header  detail lines  summary (footer)  Report format  tabular in nature  each row represents one entity (e.g. student)  similar pieces of data (e.g. mark) in a column  header has a title and a heading for each column  summary may be columnar or free-form

COSC 1P02 Introduction to Computer Science 8.23 ReportPrinter  Support for printed reports in columnar format  title for report centered at top of page  data written to field  field has a name, a label and a width  name used to specify field when writing  label forms part of heading  width is width of column  report designed by setting title and adding fields  fields added L-R across report  handles moving to next line and pagination  Methods  setting title  adding fields  writing into fields  Example  PDFCreator

ReportPrinter Methods

COSC 1P02 Introduction to Computer Science 8.25 The End