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APS105

Introduction

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Welcome

• To University and UofToronto

• To Engineering

• To APS105

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About your Prof

• Prof. Greg Steffan– PhD Computer Science, Carnegie Mellon, 2003– BASc/MASc, ECE, UofToronto, 1995/1997

• Research– Making multicores and FPGAs easier to program

• Contact:– steffan@eecg.toronto.edu– Office: EA321– Office hours: wed 12-1pm

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Why Learn About Programming and C?

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Why Learn Programming?

• Computers: our most powerful technology– Learn to command them to do your bidding!

• For love of design– Programming is pure design with few limitations– “only slightly removed from pure thought-stuff”

• Entrepreneurial opportunities– Start a company in your bedroom with no $$$

• Many engineering jobs involve programming– Simulations, databases, websites– Whether civil, electrical, mechanical…

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Why Learn C?

• Lots of other newer, sexier languages– Java, Python, Ruby, javascript

• Benefits of C:– “Compiled language”, not “interpreted”

• Close to the hardware with no layers between• Easier to understand what is happening• Important building-block for later computing courses

– C/C++ still very common• In high-performance applications• In low-level code like operating systems, databases,…

– C-like-syntax found in many of above languages

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Why Attend Lectures?

• To see someone else think through problems– Different than simply seeing the solution

• Learn “why”, not just “how”– how course material fits in with “big picture”

• Will provide proper emphasis– Highlight key material– Overview-only sundry material

• Will teach material in order of importance– Eg., order that you need it for labs

• Ideally more entertaining than reading manual– Else Prof-fail.

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Administration

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Course Website

• Portal.utoronto.ca– APS105FALL 2011

• Any Handouts– Lab Assignments– Past Exams– Form for missed labs/quizzes– Form for misgraded midterm

• Discussion Board

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Course Meetings• Lecture Periods:

– three one-hour lectures per week– Start at 10mins after the hour

• Optional Lecture:– review of regular lecture material– attendance recommended for non-experts– tuesdays 3-4pm MC102 (entire course invited)

• Tutorial Periods:– One per week, run by TAs– Quizes in about half of the tutorials– Attendance optional, unless there is a quiz

• Lab Periods:– Two hours per week– TAs available to answer questions– Attendance "mandatory"

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Evaluation

• Quizzes: 8%– 4 total– Given in tutorials– Based on lecture material since last quiz

• Labs: 17%– 8 total

• Midterm: 25%• Final Exam: 50%

– Emphasis on 2nd half of course

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Lecture Slides and Note-Taking

• Electronic slides with fill-in-the-blanks– A hybrid between powerpoint and chalkboard

• Pptx/pdf available on www prior to lecture– Please print and bring to class

• The filled-in “blanks” are only during class– Filled-in slides will not be published

• The symbol that indicates a blank to fill

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Course Textbook

• “An Introduction to Computer Science Using C”, 2nd Edition– by John Carter– Published by McGraw Hill-Ryerson

• How to get a copy:– UofT bookstore– basement of Sandford Fleming Building– Amazon etc.

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Labs (programming assignments)

• There are 8 of them in total– You will always be working on one

• Must run properly on ECF systems– Even if it runs fine elsewhere

• Marks for functionality and style– Proper style will be defined throughout term

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Cheating/Copying

• Easy to do, equally easy to catch!– “cheater-beater” software

• Automatically compares all submissions

– we do actually do this, and do follow through!• the interview and punishment process is painful for all!

• You only cheat yourself– Labs worth 1.6% each– The practice you get by doing them is invaluable– The consequences for being caught are harsh

• See Engineering Calendar for details

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Getting Help

• See course info handout• Meet some friends: “study groups”

– Collaborating vs cheating

• Ask questions in class– Point out confusing things and mistakes!

• Get help quickly if you get into trouble– First-year office (1st floor Galbraith Building)– www.calss.utoronto.ca

• Help with academics, personal

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In-Class Etiquette

• Be on time– Class starts at 10mins after the hour

• Quiet please!– Silence yourself and all electronic devices!

• Pay attention– Eg., watching youtube on laptop distracts others

• Ask questions and point out errors!– Raise your hand– Say “question!” if I don’t notice

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How to Succeed at APS105

• Attend lectures– take notes, ask questions

• Do labs yourself, on-time– Practice/experience is invaluable

• Review lecture material regularly– Be better prepared for quizes/midterm/final– Avoid last-minute cramming

• Prepare for midterm/final– Practice by trying past midterms/finals– Practice by filling lecture slides on your own

• Both available on www

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How to Succeed at Skule (computing)

• Learn to keyboard properly!• Learn unix/linux basics

– see the unix handout• has details on how to log in from home

• Learn some javascript– For programming www page features

• Write a simple app for your own use– Eg., for your laptop or iphone

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Computer Systems Basics

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Computer Systems Stack

ApplicationsJava (and others)Java interpreter (JVM, and others)C (and others) APS105

C CompilerProcessorsLogic gatesTransistorsElectrons and materials

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How We Tell a Processor What to Do

Programmer Machine Instructions

Add r3,r3,r1Cmp r3,r1Bge 0x3340aMulu r3,r5,r2Sub r1,r3,r4…

intFoo (int x){ return x + 5;}…

Compiler

Processors execute machine instructions encoded in binary

Processor

0100101

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A TYPICAL PC

Motherboard (CPU, MEMORY)Hard drive

CD/DVD R/W

USB Connectors

Graphics card

Monitor

Keyboard

Mouse

Power Supply

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Simple View of a Motherboard

Memory (RAM)

CPU

• Memory: – holds bits– can be read from or written to

• CPU: – datapath: arithmetic/logic units (add, sub), etc.– control circuitry

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C

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About C

• Invented in Bell Labs (in 1970s)– by Dennis Ritchie– Inherits from earlier language

• called “B”

• C++ – an extension of C– Supports “object oriented programming”

Dennis Ritchie

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Hello World

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Alternative Hello World

.

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GCC• gcc

– Means “GNU C compiler”– A program that converts C to 0’s & 1’s

• Stored in a file called an “executable”

• Type this command to compile hello.c

• Generates the executable file

• Insteady you could type:

• Generates the executable file

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Value Representation

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Bits and Bytes

• “bit” is short for “binary digit”– A bit can be 0 or 1

• Why do computers use bits?

• A byte is a group of 8 bits– 1 byte can be written as 1B

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RECALL: BASE 10 (decimal)

• 956

• NOTE: not all languages/cultures use base10– Ndom, Frederik Hendrik Island: base6– nimbia: base12– Huli, Papua New Guinea: base15– Tzotzil, Mexico: base20– Computers use base2 (binary)

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USING BINARY (BASE 2)

• denoted by ‘0b’ (in this course, in C-code)• Converting from binary to decimal:

• 0b1011

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Questions

• How many decimal numbers can you represent with N bits?

• NOTE: – computers can only represent finite numbers!

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Byte Size

• 1byte = 1B = 8bits

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What is this?

10010010

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Types

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Types

• Data Type: – tells computer how to interpret a group of bits– Without a type they are just bits!

• C has types:– Basic data types: built-in, already defined for

you– User-defined types: name your own! (later)

• Basic data types:– A single value of a certain size (bytes)– Example: a number or a character

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Integer Types

• int: 32bits, values: -231 .. 231-1– We will almost always use int in this class

• Other integer types:– unsigned int: 32bits, values 0.. 232-1– short: at least 16bits– long: at least 32bits– long long: at least 64bits– what does "at least" mean?

• the actual size can depend on the system!!!!!

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Floating Point Types

• How to use binary to represent real numbers?– Eg., 1.3333333333333….– Can’t: approximate, with limited accuracy

• Floating-point: a common approximation– A value (mantissa) and an exponent– Flexible: can represent very big or very small

• Eg., 2.1313*1020 or 2.1313*10-20

– We don’t need to know the details for this class

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Floating Point Types in C

• double: at least 64 bits• We will almost always use double in this class

• float: at least 32 bits

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Character Type

• representing keyboard characters: – Eg: a,b,c,d…A,B,C,D, !@#$%– Standard encoding called ASCII:

• eg., ‘A’ = 65 = 0100 0001 (binary)

• char: 8 bits, typically ASCII-encoded• Note1: char holds only a single character

– How can we represent a “string” of characters?

• Note2: recall “escapes”– Eg., ‘\n’ represents the return character

• Encoded as a single ASCII value

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Boolean Type

• Often you want to represent true/false– The old way: use int values 0 and 1– The new way: use the bool type

• bool type– Has values ‘true’ and ‘false’– Note: you have to include the bool library

• in program (at top): #include <stdbool.h>

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Identifiers and Variables

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Identifiers

• Identifiers give names to things– Choosing good names is a key skill!

• Rules: identifiers can be– any length (any number of characters)– upper & lower case letters, digits, ‘_’– First character cannot be a digit– Cannot match a C “reserved” word (like “int”)

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Choosing Identifiers: Good Style

• Use upper-case to separate words:

• Or use underscores to separate words:

• Avoid easily-confused characters:

• Choosing good identifiers is an art:

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Declaring Variables

• Variable: storage of a value of a certain type• Variable declaration:

– specifies that you plan to use a variable– and you would like it to be a certain type– Note: the C-compiler creates storage for it

• General form:

<type> <identifier list>;

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Declaring Variables: Examples

• Example declarations:

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Assigning Values

• Can assign a value at declaration, or later• Example assignment at declaration:

• Example assignment at a later point:

• Accuracy:

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Output

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Printing to the Screen on PC

Motherboard (CPU, MEMORY)Hard drive

CD/DVD R/W

USB Connectors

Graphics card

Monitor

Keyboard

Mouse Power Supply

.

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Printing Values

• the printf function prints to the screenprintf(“hi mom\n”);

• printf can also print variable valuesint age = 39;printf(“I am %d years old\n”,age);.

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Printing Integers

• decimal (base10)– %d: print the decimal using space as necessary– %4d: print the decimal using at least 4 spaces

• Example:.

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Printing chars

• char– %c: print a single character

• Example:.

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Printing doubles

• %lf– means “long float” (d is already used!)– by default prints 6 digits right of the decimal– cheat: can use %f instead, does the same thing

• %.2lf– print 2 digits right of the decimal

• %6.2lf– minimum of 6 digits, 2 right of decimal

• %e– use exponent form: ±x.xxxxxxe±nn

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Printing doubles: Examples

• Examples:.

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Printing bool

• No conversion specification for bool– Just use %d (decimal)– Prints 0 for false and 1 for true

• Example:.

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Special Cases

• How do you print ‘%’?– The ‘%’ is the ‘escape’ for conversion specs!– Answer: use ‘%%’

• Example:.

• How do you print ‘\’?– The ‘\’ is also an ‘escape’ character– Answer: use ‘\\’

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Input

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Input from the Keyboard

Motherboard (CPU, MEMORY)Hard drive

CD/DVD R/W

USB Connectors

Graphics card

Monitor

Keyboard

Mouse Power Supply

.

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Input from the Keyboard: scanf

• the scanf function inputs from the keyboard

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Inputting Multiple Values

• scanf automatically skips whitespace– eg., spaces, tabs, newlines

• .

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Consuming Whitespace

• If input string is:– “ 22 33 44”

• And I execute:– scanf(“%d%d”,&x,&y);

• The next scanf call would start at this point:– “ 22 33 44”

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Skipping Characters

• Can manually skip specific characters– eg., non-whitespace– include them in the control string

• Example:.

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Inputting Chars

• Example:int year;char term;scanf(“%d%c”,&year,&term);

• Note: %c does not skip whitespace!• .

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Constants

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Constants

• A constant is a value that does not change– possibly used in multiple places in your program

• Literal constant: – the value is written directly in your code– example: int age = 2;

• named constant:– assign a constant value an identifier– then use the identifier in your code– Named constants make for easier-to-read code!

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Named Constants Example

• With literal constant:.

• With named constant:.

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Two Methods for Named Constants

• Using the const attribute– General form:

const <type> <identifier> = <value>;

const double PI = 3.14159;– const attribute promises value will not change

• Using the #define compiler directive#define PI 3.14159– note1: directives go at top of file– note2: directives have no ‘=‘, no ‘;’– compiler does a search-and-replace of PI

• with the value 3.14159 everywhere PI appears

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Named Constants for Good Style

• avoid magic numbers in your code– numbers which have no meaning to others– use of magic numbers will cost you points in labs!

• avoid multiple copies of the same value– if you must update the value, only have to do it in

one place in the code

• Convention/Good-Style:– use capital letters for named constant identifiers– eg., PI and MAX_ATTEMPTS