week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive...

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week5 Tommy MacWilliam Pointers Memory Quiz 0 Review week5 Tommy MacWilliam [email protected] October 10, 2011

Transcript of week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive...

Page 1: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

week5

TommyMacWilliam

Pointers

Memory

Quiz 0 Review week5

Tommy MacWilliam

[email protected]

October 10, 2011

Page 2: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Announcements

I quiz0: 10/12 during lecture, not in SandersI one (double-sided) page of notes allowed

I pset3: returnedI pset4: Friday

Page 3: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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Pointers

Memory

Quiz 0 Review

Today

I Common pset3 mistakesI Pointers and memory reviewI quiz0 review

Page 4: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Hacker Tip of the Week

I looking for a file? you can always find itI find ~jharvard -name test.c

I ~jharvard: where to start lookingI -name of file

Page 5: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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Hacker Tip of the Week

I find ~/pset3 -name fifteen -type dI -type of item is a directory

I find ~/pset4 -name sudoku -exec /bin/rm ’’ \;I rm every file called sudoku

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Pointers

Memory

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pset3

I binary search can be done iteratively or recursiveI algorithm doesn’t change, but implementation details

can!

Page 7: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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Pointers

Memory

Quiz 0 Review

pset3

I example time!I search1.c, search2.c, search3.c

Page 8: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

pset3

I magic numbersI important, srsly.

I don’t forget about && and ||

if (x < 9) if (y < 9)

if (x < 9 && y < 9)

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Pointers

Memory

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Syntax

I &: address ofI where is the variable located in memory?

I *: dereferenceI given a location, go to address to get/set contents

I arrays are just pointers to the first element

Page 10: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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Pointers

Memory

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Pointers

// create a variableint i;// create a pointerint* p;// set the value of ii = 5;// make p point to ip = &i;// change the contents of what p points to*p = 50;

Page 11: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Pointers

char x = ’a’;char* y = &x;// address of x (char*)&x;// also the address of x (char*)y;// address of y (char**)&y;// value of xx;// also the value of x, because y points there*y;// ???*x;

Page 12: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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Pointers

Memory

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Stack

I local variables are placed on the stackI each function has its own stack frame, which is

inaccessible when the function returnsI grows upward

Page 13: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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Pointers

Memory

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Heap

I separate from the stackI values persist even if function returns

I until you explicitly call free()

I allocate space with mallocI get back the address of the memory you requested

I free everything you mallocI other programs need that memory!

Page 14: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

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Memory

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Pointers as Arrays

int x = 5;int* p = malloc(2 * sizeof(int));*p = 1;p[1] = 2;free(p);

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Reusing Pointers

int x = 5;int* p = malloc(2 * sizeof(int));free(p);p = &x;

Page 16: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Memory Leaks

I forget to call free? memory leak!

for (int i = 0; i < 5; i++) int* p = malloc(sizeof(int));*p = i;

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TommyMacWilliam

Pointers

Memory

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Topics

I binary numbersI compiling codeI if, else, while, forI functions, arguments, return values, recursionI variable types and scopeI stack and heapI searching and sortingI asymptotic notationI pointers

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Pointers

Memory

Quiz 0 Review

Binary

42

0 0 1 0 1 0 1 027 26 25 24 23 22 21 20

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Pointers

Memory

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Compiling Code

I make sudokuI looks in Makefile for sudokuI runs gcc to create binaryI binary is executable

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Pointers

Memory

Quiz 0 Review

Functions

int function(int argument1, float argument2) // do stuffint r = 5;return r;

int x = function(5, 3.14);

Page 21: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

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Variables

I char: 1 byte, characterI int: 4 bytes, integerI float: 4 bytes, floating-point decimalI int*, char*: 4 bytes, pointerI double: 8 bytes, bigger decimalI long long: 8 bytes, bigger integer

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Memory

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ASCII

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Pointers

Memory

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Casting

I float y = 1.5; int x = (int)y;I char a = ’a’; int b = ’a’ + 1;I int c = atoi(“50”);I int d = round(50.5);

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TommyMacWilliam

Pointers

Memory

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Stack and Heap

I stack: local variablesI each function gets its own stack frameI function returning means stack frame is inaccessible

I heap: malloc’d variablesI persist until you explicitly free them

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Stack and Heap

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TommyMacWilliam

Pointers

Memory

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Searching

I linear search: look at every single elementI O(n), Ω(1)I does not require sorted list

I binary search: keep looking at middle elementI O(log n), Ω(1)I requires sorted list

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Memory

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Sorting

I bubble sort: if elements are out of place, swap themI O(n2), Ω(n)

I selection sort: find minimum, put it at the beginning ofthe list

I O(n2), Ω(n2), Θ(n2)

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Pointers

Memory

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Common Running Times

I in ascending order:I O(1): constantI O(log n): logarithmicI O(n): linearI O(n log n): linearithmicI O(nc): polynomialI O(cn): exponentialI O(n!): factorial

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Pointers

Memory

Quiz 0 Review

Questions

IAmA CS50 TF. AMA.

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Practice Problems (Doug Lloyd)

I based on the following giveGrade function, why iseveryone unhappy with their grade?

Page 31: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Practice Problems (Doug Lloyd)

char giveGrade(int quizScore) char letterGrade;switch(quizScore)

case 100: case 90:letterGrade = ’A’;

case 80:letterGrade = ’B’;

case 70:letterGrade = ’C’;

case 60:letterGrade = ’D’;break;

default:letterGrade = ’F’;

return letterGrade;

Page 32: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

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Practice Problems (Doug Lloyd)

I wtf does this do?

int secret(int x, int y) if (y == 0)

return 1;else

return x * secret(x, y-1);

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Practice Problems (Doug Lloyd)

I Write a function div_by_n() which takes twoarguments, k and n, and returns true if k is divisible byn, and false otherwise.

I Write the few lines of C code that would print out themultiplication table from 1 to 10.

Page 34: week5 Tommy MacWilliam Pointers week5 · pset3 I binary search can be done iteratively or recursive I algorithm doesn’t change, but implementation details can! week5 Tommy MacWilliam

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TommyMacWilliam

Pointers

Memory

Quiz 0 Review

Practice Problems (Doug Lloyd)

I Imagine I execute the following lines of code:

string input = GetString();string input_copy = input;input_copy[0] = ’X’;

I Why is it that, if I look at input[0], it is also ’X’, eventhough our line of code modified input_copy?

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TommyMacWilliam

Pointers

Memory

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Practice Problems

I 2010I 2-3, 11, 15, 28, 30, 33

I 2009I 22-24, 27

I 2008I 3, 6, 13, 15-17

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Pointers

Memory

Quiz 0 Review

Questions

Last chance.


Ts2012, week5

Ts2012, week5

Week5 Triggers

Week5 Triggers

Business2 week5

Business2 week5

Week5 chap6

Week5 chap6

Week5 NoiseandMatchedFilters ...wireless-systems.ece.gatech.edu/4601/lectures-2016/week5.pdf · EE4601 Communication Systems Week5 NoiseandMatchedFilters ErrorProbabilitywithBinarySignaling

Week5 NoiseandMatchedFilters ...wireless-systems.ece.gatech.edu/4601/lectures-2016/week5.pdf · EE4601 Communication Systems Week5 NoiseandMatchedFilters ErrorProbabilitywithBinarySignaling

Git Magic: Versioning Files Like a Boss - CS50cdn.cs50.net/2011/fall/seminars/Git_magic/Git_magic.pdfGit Magic: Versioning Files Like a Boss Tommy MacWilliam tmacwilliam@cs50.net Today

Git Magic: Versioning Files Like a Boss - CS50cdn.cs50.net/2011/fall/seminars/Git_magic/Git_magic.pdfGit Magic: Versioning Files Like a Boss Tommy MacWilliam [email protected] Today

News Week5

News Week5

Week5 – Schema

Week5 – Schema

การออกแบบและพัฒนาโปรแกรม Week5

การออกแบบและพัฒนาโปรแกรม Week5

pset3: Fifteen findd2o9nyf4hwsci4.cloudfront.net/2011/fall/psets/3/walkthrough3.pdf · pset3: Fifteen Tommy MacWilliam Generate Makefiles find Fifteen pset3: Fifteen Tommy MacWilliam

pset3: Fifteen findd2o9nyf4hwsci4.cloudfront.net/2011/fall/psets/3/walkthrough3.pdf · pset3: Fifteen Tommy MacWilliam Generate Makefiles find Fifteen pset3: Fifteen Tommy MacWilliam

Week5 analys

Week5 analys

Comparative Guide to Nutritional Supplements by Lyle MacWilliam

Comparative Guide to Nutritional Supplements by Lyle MacWilliam

Week5 analys0096

Week5 analys0096

Git Magic: Versioning Files Like a Bossd2o9nyf4hwsci4.cloudfront.net/.../Git_magic.pdf · Git Magic: Versioning Files Like a Boss Tommy MacWilliam tmacwilliam@cs50.net. Today ...

Git Magic: Versioning Files Like a Bossd2o9nyf4hwsci4.cloudfront.net/.../Git_magic.pdf · Git Magic: Versioning Files Like a Boss Tommy MacWilliam [email protected]. Today ...

Technology and Health - myhealthyhome.com€¦ · USANA Health Sciences Submitted by: Lyle MacWilliam, MSc, FP MacWilliam Communications Inc. 7594 Klinger Road Vernon, British Columbia

Technology and Health - myhealthyhome.com€¦ · USANA Health Sciences Submitted by: Lyle MacWilliam, MSc, FP MacWilliam Communications Inc. 7594 Klinger Road Vernon, British Columbia

Reading week5

Reading week5

Tommy MacWilliam · 2018. 4. 12. · Tommy MacWilliam Functions Scope Magic Numbers Arrays main Crypto Practice Problems Functions I type: any variable type, like float, int, or string

Tommy MacWilliam · 2018. 4. 12. · Tommy MacWilliam Functions Scope Magic Numbers Arrays main Crypto Practice Problems Functions I type: any variable type, like float, int, or string

x_tremes week5

x_tremes week5

ELT J 1986 MacWilliam 131 5

ELT J 1986 MacWilliam 131 5

Week5 Brother

Week5 Brother