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CSC-201 - Computer Science ILecture #4: Chapter 6

Dr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck CartledgeDr. Chuck Cartledge

September 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pmSeptember 12, 2016 at 5:09pm

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Table of contents I

1 Test overview

2 Test

3 Schedule

4 Miscellanea

5 Chapter 6

6 Q & A

7 Conclusion

8 References

9 Files

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This is it.

Cover chapters 1 through 5(inclusive)

Exam has been written yet

Exam should take about anhour and 15.

One letter sized sheet ofpaper as “cheat sheet”

When finished with exam,leave room with answers

Lecture will start after examends

Any questions? Almost too late.

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The beatings will continue until morale improves.

You’ve got:1 hour 15 minutes

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Schedule for the semester

Wk. Date Topic Wk. Date Topic1 08/22 Chaps. 1 – 2 X 9 10/17 Chap. 102 08/29 Chaps. 3 – 4 X 10 10/24 Chaps. 10 – 113 09/05 Chap. 5 X 11 10/31 Chaps. 10 – 114 09/12 Test – Chap. 6 12 11/07 Test– Chap. 145 09/19 Chap. 7 13 11/14 Chap. 146 09/26 Chap. 8 14 11/28 Chap. 187 10/03 Chap. 9 15 12/05 Chap. 188 10/10 Test – Chap. 10 16 12/12 Exam

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Corrections and additions since last lecture.

Updated assignment #02included files

Homework for chapter 5 duebefore class

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This and that

Read from a file.

Objectives are fairlystraightforward:

Read strings from a datafile.

First string is the key.

Second string is the plaintext.

Output plain and“encrypted” strings to thescreen in a particular order

Submit your source code.

This is a single person effort (nota team effort).

Any questions or problems?

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Looping

Basic looping structures

while loopwhile ( conditional) { statements with changer}for loopfor (initial; conditional; changer) { statements}do ...while loopdo { statements with changer} while (conditional)Handcrafted (which we won’t go into)

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Looping

What is a loop and why do we care?

“A loop executes the same statement (simple orcompound) over and over again, as long as a condition orset of conditions is satisfied.”

Dale and Weems [2]

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Looping

Loop taxonomy

Classical ways of classifying looping structures:

Count controlled Repeat statement(s) aspecified number of times

Event controlled Repeat statement(s) until a“stop” repeating conditionis reached

We’ll look at the different types of looping statements as count orevent controlled structures.

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Looping

The event controlled while loop

1 The conditional is evaluated.

2 If the conditional is FALSEthen branch out

3 Execute the statements inblock

4 Repeat

The statements in the block maynever be executed.

Image from [4].

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Looping

Same image.

Image from [4].

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Looping

The count controlled while loop

A counter is initialized

1 The conditional is evaluated(usually based on thecounter)

2 If the conditional is FALSEthen branch out

3 Execute the statements inblock

4 Update the counter

5 Repeat

The statements in the block maynever be executed.

Image from [3].

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Looping

Same image.

Image from [3].

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Looping

The do . . . while loop

1 Execute the statements inblock

2 The conditional is evaluated

3 If the conditional is FALSEthen branch out

4 Repeat

The statements in the block willalways be executed at least once.

Image from [3].

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Looping

Same image.

Image from [3].

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Looping

Comparing different looping constructs

Image from [3]. The different structures have different shapes.

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Looping

Comparing different looping constructs doing the samething

Image from [3]. Other implementations are possible.

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Expanding on event controlled looping

Different kinds of controlling events

Sentinel Keep processing data until aspecial value that is not apossible data value isentered to indicate thatprocessing should stop

End-of-file Keep processing data aslong as there is more data inthe file

Flag Keep processing data untilthe value of a flag changesin the loop body

We’ll look at each of these different types.

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Expanding on event controlled looping

A simple scenario

There is a data file myInfile that contains blood pressuremeasurements.1

The data file has some special/interesting values:

There may be exactly 100 readings.

There may be some unknown number of readings.

There may be a special value (-1) that means stop reading.

There may be out of range data (>= 200) that means stopreading.

We’ll look at how to handle these cases individually.

1Example taken from slide deck provided by JB Learning.

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Expanding on event controlled looping

Count controlled loop

Read exactly 100 values from the file.

std::string fileName = "/tmp/temp.txt";

std::ifstream inputFile;

int data;

inputFile.open(fileName.c_str());

for (int i = 0; i < 100; i++)

{

data

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Expanding on event controlled looping

End-of-file controlled loop

Read all the data from the file.

std::string fileName = "/tmp/temp.txt";

std::ifstream inputFile;

int data;

inputFile.open(fileName.c_str());

while(inputFile)

{

data

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Expanding on event controlled looping

Sentinel controlled loop

Read all the data from the file until a special value is read.

std::string fileName = "/tmp/temp.txt";

std::ifstream inputFile;

int data = 0;

inputFile.open(fileName.c_str());

for (; data > -1 ;)

{

data

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Expanding on event controlled looping

Flag controlled loop

Read all the data from the file until a special value is read.

std::string fileName = "/tmp/temp.txt";

std::ifstream inputFile;

int data = 0;

inputFile.open(fileName.c_str());

for (; data < 200 ;)

{

data

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Expanding on event controlled looping

The “infinite” loop

There may be times when you want a loop to repeat, but theterminate conditions are too hard to make into a set ofcomparisons.std::string fileName = "/tmp/temp.txt";

std::ifstream inputFile;

int data = 0;

inputFile.open(fileName.c_str());

for (; ;) {

data

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Expanding on event controlled looping

Nesting looping control structures

Looping structures can be“nested” one inside the other.The only rule is that the innerlooping structure has to becompletely inside the outerstructure.

Image from [1].

Looping structures can be nested as deeply as makes sense. (SeelineCt.cpp in source files for example.)

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Q & A time.

“’The Answer to the GreatQuestion . . . Of Life, the Universeand Everything . . . is. . . forty-two,’ said DeepThought, with infinite majestyand calm.”Douglas Adams, TheHitchhiker’s Guide to theGalaxy

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What have we covered?

Test #01Covered looping statements indifferent formsTalked about assignment #002Assignment #002 and Chapter 6homework before class

Next time: Chapter 7 (and return tests)

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References I

[1] Russ Burlingame, Catch all these evolving pokemon nesting dollgraphics, http://comicbook.com/2015/09/16/catch-all-these-evolving-pokemon-nesting-doll-graphics, 2015.

[2] Nell Dale and Chip Weems, Programming and problem solvingwith c++: Comprehensive, Jones & Bartlett Publishers, 2013.

[3] EduGrabs Staff, Difference between for while and do while loopin c++, http://www.edugrabs.com/difference-between-for-while-and-do-while-loop-in-c/, 2015.

[4] TutorialsPoint Staff, C++ while loop, http://www.tutorialspoint.com/cplusplus/cpp_while_loop.htm.

http://comicbook.com/2015/09/16/catch-all-these-evolving-pokemon-nesting-doll-graphicshttp://comicbook.com/2015/09/16/catch-all-these-evolving-pokemon-nesting-doll-graphicshttp://www.edugrabs.com/difference-between-for-while-and-do-while-loop-in-c/http://www.edugrabs.com/difference-between-for-while-and-do-while-loop-in-c/http://www.tutorialspoint.com/cplusplus/cpp_while_loop.htmhttp://www.tutorialspoint.com/cplusplus/cpp_while_loop.htm

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Files of interest

1 Edgar Dijkstra’s letterabout the GOTO statement

Edgar Dijkstra: Go To Statement Considered Harmful

1

Edgar Dijkstra: Go To Statement Considered Harmful

Edgar Dijkstra: Go To Statement Considered Harmful

2

Aus: Communications of the ACM 11, 3 (March 1968). 147-148.

"Chuck Cartledge"

Test overviewTestScheduleMiscellaneaCorrections and additions since last lecture.This and that

Chapter 6LoopingExpanding on event controlled looping

Q & AConclusionReferencesFiles