PowerPoint PresentationNumber review...Introduction to CHas there been an update to ANSI C?DisclaimerCompilation : OverviewCompilation : AdvantagesCompilation : DisadvantagesC Syntax: mainC Syntax: Variable DeclarationsAddress vs. ValuePointersSlide 13Slide 14Pointers and Parameter PassingSlide 16Slide 17Peer Instruction QuestionAnd in conclusion…Reference slidesAdministriviaAdministrivia : You have a question?C vs. Java™ Overview (1/2)C vs. Java™ Overview (2/2)C Syntax: True or False?C syntax : flow controlCS61C L03 Introduction to C (pt 1) (1)Garcia, Spring 2008 © UCBLecturer SOE Dan Garciawww.cs.berkeley.edu/~ddgarciainst.eecs.berkeley.edu/~cs61c CS61C : Machine Structures Lecture 3 – Introduction to the C Programming Language (pt 1) 2008-01-28Hello to Dev Anand from Pune, Maharashtra, INDIA Infected Frames! Malware has been foundin photo frames recently sold by Best Buy. This is not the first time this has happened in personal electronics (iPods, drives, MP3 players). Be careful! www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/01/26/MNE7UHOOQ.DTLCS61C L03 Introduction to C (pt 1) (2)Garcia, Spring 2008 © UCBNumber review...•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 ...META: We often make design decisions to make HW simpleCS61C L03 Introduction to C (pt 1) (3)Garcia, Spring 2008 © UCBIntroduction to CCS61C L03 Introduction to C (pt 1) (4)Garcia, Spring 2008 © UCBHas there been an update to ANSI C?•Yes! It’s called the “C99” or “C9x” std•You need “gcc -std=c99” to compile•Referenceshttp://en.wikipedia.org/wiki/C99http://home.tiscalinet.ch/t_wolf/tw/c/c9x_changes.html•Highlights•Declarations anywhere, like Java (#15)•Java-like // comments (to end of line) (#10)•Variable-length non-global arrays (#33)•<inttypes.h>: explicit integer types (#38)•<stdbool.h> for boolean logic def’s (#35)•restrict keyword for optimizations (#30)CS61C L03 Introduction to C (pt 1) (5)Garcia, Spring 2008 © 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 referenceCheck online for more sources•“JAVA in a Nutshell,” O’Reilly. Chapter 2, “How Java Differs from C”•Brian Harvey’s course notesOn class websiteCS61C L03 Introduction to C (pt 1) (6)Garcia, Spring 2008 © 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.•These differ mainly in when your program is converted to machine instructions.•For C, 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) (7)Garcia, Spring 2008 © 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) (8)Garcia, Spring 2008 © 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 “changecompilerun [repeat]” iteration cycle is slowCS61C L03 Introduction to C (pt 1) (9)Garcia, Spring 2008 © 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). Here argc is 2: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) (10)Garcia, Spring 2008 © 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; if not, it holds garbage!•Examples of declarations:•correct: {int a = 0, b = 10;...•Incorrect:* for (int i = 0; i < 10; i++)*C99 overcomes these limitationsCS61C L03 Introduction to C (pt 1) (11)Garcia, Spring 2008 © UCBAddress vs. Value•Consider memory to be a single huge array:•Each cell of the array has an address associated with it.•Each cell also stores some value.•Do you think they use signed or unsigned numbers? Negative address?!•Don’t confuse the address referring to a memory location with the value stored in that location.23 42 ... ...101 102 103 104 105 ...CS61C L03 Introduction to C (pt 1) (12)Garcia, Spring 2008 © UCBPointers•An address refers to a particular memory location. In other words, it points to a memory location.•Pointer: A variable that contains the address of a variable.23 42 ... ...101 102 103 104 105 ...xyLocation (address)namep104CS61C L03 Introduction to C (pt 1) (13)Garcia, Spring 2008 © UCBPointers•How to create a pointer:& operator: get address of a variableint *p, x; p ? x ?x = 3; p ? x 3p =&x; p x 3•How get a value pointed to? * “dereference operator”: get value pointed toprintf(“p points to %d\n”,*p); Note the “*” gets used 2 different ways in this example. In the declaration to indicate that p is going to be a pointer, and in the printf to get the value pointed to by p.CS61C L03 Introduction to C (pt 1) (14)Garcia, Spring 2008 © UCBPointers•How to change a variable pointed to?•Use dereference * operator on left of =p x 5*p = 5;p x 3CS61C L03 Introduction to C (pt 1) (15)Garcia, Spring 2008 © UCBPointers and Parameter Passing•Java and C pass parameters “by value”•procedure/function/method gets a copy of the parameter, so changing the copy cannot change the original void addOne (int x) { x = x + 1;} int y
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