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CSC-201 - Computer Science ILecture #7: Chapter 9

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

October 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20amOctober 4, 2016 at 11:20am

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Table of contents I

1 Schedule

2 Miscellanea

3 Chap. 9

4 Break

5 Test preps.

6 Hands on

7 Q & A

8 Conclusion

9 References

10 Files

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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 X 12 11/07 Test Chap. 145 09/19 Chap. 7 X1 13 11/14 Chap. 146 09/26 Chap. 8 X 14 11/28 Chap. 187 10/03 Chap. 9 15 12/05 Chap. 188 10/10 Test Chap. 10 16 12/12 Exam

Notes:

1 Class canceled due to electrical fire in instructors home

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Programming assignment #003

File Based Address Book

Objectives are fairly straightforward:

Accept commands from the user

Read strings from a data file

Search strings for data from user

Output strings to the screen in aparticular format, or outputmessage

Submit your source code.

This is a single person effort (not ateam effort).

Due by start of class 5 Oct. 2016.

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Programming assignment #003

Q & A time.

Q: Whats a light-year?A: One-third less calories than aregular year.

Now is the time to ask questions.

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Corrections and additions since last lecture.

Graded all homework to date

Homework for chapters 7and 8 due before class today

Started gradingprogramming assignment#003

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Scope and lifetime

Nothing lives forever

We can create programs that aregreat and wonderful, but:

1 They all have a begining andan end.

2 Each part of them has theirown life.

3 Each part of them can haveparents and children.

Image from [1].

Today we will talk about the life of variables. Called scope

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Scope and lifetime

Definitions

The scope of an identifier (or named constant) is the region ofprogram code in which it is legal to use that identifier for anypurpose.Types of scope:

Local : The scope of an identifier that is declared inside ablock (this includes function parameters) extends fromthe point of declaration to the end of the block

Global : The scope of an identifier that is declared outside of allnamespaces, functions, and classes extends from point ofdeclaration to the end of the entire file containing theprogram code.

Scope[2]

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Scope and lifetime

Details about the scoping rules

1 Function names have global scope

2 A function parameters scope is identical to the scope of a localvariable declared in the outermost block of the function body

3 A global variables (or constants) scope extends from itsdeclaration to the end of the file, except as noted in rule 5

4 A local variables (or constants) scope extends from itsdeclaration to the end of the block in which it is declared,including any nested blocks, except as noted in rule 5

5 An identifiers scope does not include any nested block thatcontains a locally declared identifier with the same name(local identifiers have name precedence)

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Scope and lifetime

What does all that mean from a practical sense?

1 An identifier exists at global scope, or inside a set of curlybraces

2 The compiler looks in the current context, then outwards untilthe identifier definition is found

3 If there are identifier name conflicts, the closest one wins

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Scope and lifetime

Namespaces are another wrinkle.

Only one entity can exist with a particular name in aparticular scope. This is seldom a problem for localnames, since blocks tend to be relatively short, andnames have particular purposes within them, such asnaming a counter variable, an argument, etc...But non-local names bring more possibilities for namecollision, especially considering that libraries may declaremany functions, types, and variables, neither of themlocal in nature, and some of them very generic.Namespaces allow us to group named entities thatotherwise would have global scope into narrower scopes,giving them namespace scope. This allows organizing theelements of programs into different logical scopes referredto by names.

T. Staff [3]

The scope of an identifier declared in a namespace definitionextends from the point of declaration to the end of the namespacebody, and its scope includes the scope of a using directivespecifying that namespace

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Scope and lifetime

How declare and use a namespace

How to create a namespace indentifier:

namespace csc201nameSpace{

int i;

int j;

}

How to use a namespace identifier:1 Use a qualified name consisting of the namespace, the scope

resolution operator :: and the desired the identifiercsc201nameSpace::i = 56;

2 Write a using directive locally or globallyusing namespace csc201nameSpace;

3 Write a using declarationusing std::abs;

alpha = abs(beta);

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Scope and lifetime

Memory allocation

Somethings in your source code will cause memory allocation,other things wont.Those that cause allocation, consume computer resources duringprogram execution.Those that done cause allocation, are used by the compiler while itbuilds the executable program.

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Scope and lifetime

Image from [2].

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Scope and lifetime

Image from [2].

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Scope and lifetime

Lifetime of a Variable

Some last longer than others.

The lifetime of a variable is the time during program executionin which an identifier actually has memory allocated to it

There are different types of variables

Local variables are allocated and alive while the function isexecuting. They are lost when the function terminates.Global variables are allocate and alive while the the program isexecuting. They are lost when the program terminates.Automatic variables are allocated at block entry, and lost atblock exit.Static variables remain allocated throughout the life of theprogram.

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More about functions

Our friends, pass parameters

Basically, two types of pass parameters.

Pass-by-value: the value of the variable (its contents) arepassed to the called function

Pass-by-reference: the address of the variable is passed tothe called function

Things to remember:

Pass-by-value: the called function CANNOT change thingsin the calling function

Pass-by-reference: the called function CAN change thingsin the calling function

Look at readAddressBook01.cpp from the programmingassignment.

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More about functions

Should a function return a value or not?

1 If it must return more than one value or modify any of thecallers arguments, do not use a value-returning function

2 If it must perform I/O, do not use a value-returning function

3 If there is only one value returned, and it is Boolean, avalue-returning function is appropriate

4 If there is only one value returned, and that value will be usedimmediately in an expression, a value-returning function isappropriate

5 When in doubt, use a void function; you can recode anyvalue-returning function as a void function by adding an extraoutgoing parameter

6 If both void and value-returning are acceptable, use the oneyou prefer

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Break time.

Take about 10 minutes.

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Some ideas

Broad things from different chapters

1 Loops and loops and looping again(different types and how are theydifferent)

2 Control structures (different types,different use cases)

3 Functions (their parts, theirrequirements, ways to returnthings)

4 Scoping (how long do differentthings live, are visible, and why)

5 Lots of vocabulary and orderingthings

6 More vocabulary and basic syntax

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Some ideas

There will be an exam.

Cover chapters 6 through 9(inclusive)

Exam has not been writtenyet

Exam should take about anhour(ish)

When finished with exam,leave room with answers

Lecture will start after examends

Any questions? Now is the time to ask.

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Practice exercises

Programs to load into CodeBlocks and get running:

1 scope01.cpp to look at scoping, and get our hands dirty

Others, if you have time.

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Q & A time.

Q: Why do mountain climbersrope themselves together?A: To prevent the sensible onesfrom going home.

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What have we covered?

Covered chapter 9Began to understand how somethings are short lived, while othersare longerTalked about functions in differentforms and flavors

Next time: Chapter 9 homework before class, Chapter 10

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References I

[1] Astronmical pictures, http://www.astrogb.com/index.htm,2016.

[2] Sylvia Sorkin, Programming and problem solving with c++,Teacher Resource Jones and Barlett Learning, 2014.

[3] TutorialsPoint Staff, Name visibility,http://www.cplusplus.com/doc/tutorial/namespaces/,2016.

http://www.astrogb.com/index.htmhttp://www.cplusplus.com/doc/tutorial/namespaces/

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Files of interest

1 scope01.cpp (looking at variable

scoping)

2 nameSpace.cpp (looking at

namespace variable scoping)

3 static.cpp (looking at static

variables)

4 readAddressBook01.cpp (looking at

pass by reference and value)

scope01.cpp#include

#defineDEBUG_PROGRAM

#ifdefDEBUG_PROGRAM

#defineDEBUG(a){std::clog