QMCS 230: Today in Class

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QMCS 230 Today in Class

• Homework
• Nested Loops
• Other things
• Group work if time
• Start working with files?
• Lab 8

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Homework

• Typical weekly assignments
• 1 informal lab
• Hand in source code ONLY
• Less credit than the formal lab
• Checked in general for content and form
• 1 formal lab
• E-mail source code ONLY
• Checked carefully
• Grading
• Check plus plus a few labs for special work
  think A
• Check plus almost no problems think A
• Check Some problems think of a B
• Check Minus many or major problems think of a
  C
• No Credit major parts of the assignment missing

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On the Exam

• Chapter 2, all sections except
• 2.6, 2.8
• Chapter 3, all sections except
• 3.8, 3.9
• Chapter 4, Sections 4.1-4.6
• Study the Checkpoints

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Reference Materials

• I will provide reference guides
• Java syntax basics
• Reserved words you might use
• Tables of details, if needed
• Closed book closed notes

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Nested Loops

• How would we do hhmmss ?
• What does nesting mean?
• Nothing to do with eggs.

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Break and Continue (Sec 4.8)

• Loops do all statements in order
• Break and Continue change this.
• Cause surprising behavior
• They exist, but we will NOT use them
• Makes programs harder to understand
• And harder for ME to read

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Picking a loop

• Always do it at least once?
• Maybe skip it all sometimes?
• A fixed number of times?

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Picking a loop

• Always do it at least once?
• Do - While
• Maybe skip it all sometimes?
• While
• A fixed number of times?
• For loop

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Group Work

• 8 groups - 4 problems
• ALL average 4 numbers read from keyboard
• Different problems
• Use 4 separate statements
• Use for loop
• Use do while loop
• Use while loop

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Working with Files

• We use the same methods as System.in/out
• println, print, printf, Scanner class
• We must open and close files
• Open when we create the file object
• close() method when done

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Output Files

• PrintWriter class
• new takes file name as an argument
• Creates that file
• Use the object with print methods
• Write to a file
• import java.io.
• public static void main(String args) throws
  IOException
• PrintWriter pwa
• pwa new PrintWriter(existingfile.txt)
• Example write student names

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Append to Output File

• Use an extra object for the existing file
• FileWriter object
• FileWriter fw // to define the existing file
• PrintWriter pwa // to open for print functions
• fw new FileWriter(existingfile.txt, true)
• pwa new PrintWriter(fw)

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Input Files

• Use Scanner class and File class
• import java.util.Scanner
• import java.io.
• public static void main(String args) throws
  IOException
• fn // identify the file to read
• Scanner sc // for reading the data
• fn new File(filename.txt)
• sc new Scanner(fn)

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Thats it.

• Questions?

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