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Berkeley COMPSCI 61C - Lecture Notes

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PowerPoint PresentationReview (1): OverviewReview(2): The way to remember #sDisclaimerCompilation : OverviewCompilation : AdvantagesCompilation : DisadvantagesC vs. Java™ Overview (1/2)C vs. Java™ Overview (2/2)C Syntax: Variable DeclarationsC Syntax: True or False?C syntax : flow controlC Syntax: mainAdministrivia : You have a question?Administrivia : Near termAddress vs. ValuePointersSlide 18Slide 19Pointers and Parameter PassingSlide 21Slide 22Peer Instruction QuestionPeer Instruction AnswerAnd in conclusion…CS61C L03 Introduction to C (pt 1) (1)Garcia, Spring 2005 © UCBLecturer PSOE Dan Garciawww.cs.berkeley.edu/~ddgarciainst.eecs.berkeley.edu/~cs61c CS61C : Machine Structures Lecture 3 – Introduction to the C Programming Language 2005-01-24Princeton cracks down! Previously, nearly half the grades given out were {A-,A,A+}…not unusual; other Ivys 44-55%. New cap is 35%. EECS policy is 17% (Lower div) and 23% (upper), though not strict.www.ledger-enquirer.com/mld/mercurynews/news/world/10713562.htmCS61C L03 Introduction to C (pt 1) (2)Garcia, Spring 2005 © UCBReview (1): Overview•We represent “things” in computers as particular bit patterns: N bits  2N•Decimal for human calculations, binary for computers, hex to write binary more easily•1’s complement - mostly abandoned•2’s complement universal in computing: cannot avoid, so learn•Overflow: numbers ; computers finite, errors! 00000 00001 01111...111111111010000 ...00000 00001 01111...111111111010000 ...CS61C L03 Introduction to C (pt 1) (3)Garcia, Spring 2005 © UCB•What is 227? How many bits addresses (I.e., what’s ceil log2 = lg of) 19 PiB?•Answer! 2XY means…X=0  ---X=1  kibi ~103X=2  mebi ~106X=3  gibi ~109X=4  tebi ~1012X=5  pebi ~1015X=6  exbi ~1018X=7  zebi ~1021X=8  yobi ~1024Review(2): The way to remember #sY=0  1Y=1  2Y=2  4Y=3  8Y=4  16Y=5  32Y=6  64Y=7  128Y=8  256Y=9  512MEMORIZE!CS61C L03 Introduction to C (pt 1) (4)Garcia, Spring 2005 © UCBDisclaimer•Important: You will not learn how to fully code in C in these lectures! You’ll still need your C reference for this course.•K&R is a must-have reference.-Check online for more sources.•“JAVA in a Nutshell,” O’Reilly. -Chapter 2, “How Java Differs from C”.CS61C L03 Introduction to C (pt 1) (5)Garcia, Spring 2005 © UCBCompilation : OverviewC com pilers take C and convert it into an architecture specific machine code (string of 1s and 0s).•Unlike Java which converts to architecture independent bytecode.•Unlike most Scheme environments which interpret the code.•Generally a 2 part process of compiling .c files to .o files, then linking the .o files into executablesCS61C L03 Introduction to C (pt 1) (6)Garcia, Spring 2005 © UCBCompilation : Advantages•Great run-time performance: generally much faster than Scheme or Java for comparable code (because it optimizes for a given architecture)•OK compilation time: enhancements in compilation procedure (Makefiles) allow only modified files to be recompiledCS61C L03 Introduction to C (pt 1) (7)Garcia, Spring 2005 © UCBCompilation : Disadvantages•All compiled files (including the executable) are architecture specific, depending on both the CPU type and the operating system.•Executable must be rebuilt on each new system.•Called “porting your code” to a new architecture.•The “changecompilerun [repeat]” iteration cycle is slowCS61C L03 Introduction to C (pt 1) (8)Garcia, Spring 2005 © UCBC vs. Java™ Overview (1/2)Java•Object-oriented(OOP)•“Methods”•Class libraries of data structures•Automatic memory managementC•No built-in object abstraction. Data separate from methods.•“Functions”•C libraries are lower-level•Manualmemory management•PointersCS61C L03 Introduction to C (pt 1) (9)Garcia, Spring 2005 © UCBC vs. Java™ Overview (2/2)Java•High memory overhead from class libraries•Relatively Slow•Arrays initialize to zero•Syntax: /* comment */ // commentSystem.out.printC•Low memory overhead•Relatively Fast•Arrays initialize to garbage•Syntax:/* comment */printfCS61C L03 Introduction to C (pt 1) (10)Garcia, Spring 2005 © UCBC Syntax: Variable Declarations•Very similar to Java, but with a few minor but important differences•All variable declarations must go before they are used (at the beginning of the block). •A variable may be initialized in its declaration.•Examples of declarations:•correct: {int a = 0, b = 10;...•incorrect: for (int i = 0; i < 10; i++)CS61C L03 Introduction to C (pt 1) (11)Garcia, Spring 2005 © UCBC Syntax: True or False?•What evaluates to FALSE in C?•0 (integer)•NULL (pointer: more on this later)•no such thing as a Boolean•What evaluates to TRUE in C?•everything else…•(same idea as in scheme: only #f is false, everything else is true!)CS61C L03 Introduction to C (pt 1) (12)Garcia, Spring 2005 © UCBC syntax : flow control• Within a function, remarkably close to Java constructs in methods (shows its legacy) in terms of flow control•if-else•switch•while and for•do-whileCS61C L03 Introduction to C (pt 1) (13)Garcia, Spring 2005 © UCBC Syntax: main•To get the main function to accept arguments, use this:int main (int argc, char *argv[])•What does this mean?•argc will contain the number of strings on the command line (the executable counts as one, plus one for each argument).-Example: unix% sort myFile•argv is a pointer to an array containing the arguments as strings (more on pointers later).CS61C L03 Introduction to C (pt 1) (14)Garcia, Spring 2005 © UCBAdministrivia : You have a question?•Do not email Dan (& expect response)•Hundreds of emails in inbox•Email doesn’t scale to classes with 200+ students!•Tips on getting an answer to your question:•Ask a classmate•Ask Dan after or before lecture•The newsgroup, ucb.class.cs61c-Read it : Has your Q been answered already?-If not, ask it and check back•Ask TA in section, lab or OH•Ask Dan in OH•Ask Dan in lecture (if relevant to lecture)•Send your TA email•Send one of the two Head TAs email•Send Dan emailCS61C L03 Introduction to C (pt 1) (15)Garcia, Spring 2005 © UCBAdministrivia : Near term•Upcoming lectures•C pointers and arrays in detail•HW•HW0 due in discussion tomorrow•HW1 due this Wed @ 23:59 PST•HW2 due next Wed @ 23:59 PST•Reading•K&R Chapters 1-5 (lots, get started


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