Class Objectives · The objectives of this class are as follows

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Class Objectives
· The objectives of this class are as follows:
· Teach you how to read C programs

· Teach you how to write C programs

· Teach you how to debug C programs

· Teach you how to design good C programs

· This is a class for developers, not managers

· Managers are certainly invited to attend, but they must plan to do real work

· If you are taking this class to see what C is all about without planning on really learning it and programming it, you are in the wrong class!

How to Succeed in this Class
· Attend class

· "90 percent of life is just showing up." --Woody Allen

· Exams are heavily based on material presented in class
· Never miss more than one consecutive week of classes

· If you just have to take that two week vacation, plan it so that you only miss one week of classes -- really!

· Missing even one class will severely limit your ability to keep up, particularly wrt the exams
· Read ahead
· Do the homework

· Students with a previous programming (e.g. Pascal or C++) background should plan on spending 5-10 hours per week

· Students with a no programming background but computer literate 10-20 hours per week

· Students with a no programming background and no computer experience 20-30 hours per will be spending a lot of time struggling with the tools as well as learning how to program

· The best plan of action is to do a little bit of the lab assignment work each day, particularly if you have a home computer

· The worst plan of action is to do everything the night before the homework is due

· Ask questions

How to Fail in this Class
· Miss two consecutive weeks of class sessions
· Try to survive without access to a C compiler

· You learn C by doing, i.e., you must write C programs, compile them, and run them

· Never spend any time on this outside of class
· Do not attempt any of the homework
· Habitually show up late for class or habitually leave early
· The bottom line is that you will get out of this class what you put into it!!!
· To succeed, you need to spend at least 5 to 10 hours per week on your own

Overview of a Computer - Hardware
Reference: Brooks, Chapter 1; KP, Chapter 1

  • Central Processing Unit (CPU) controls the flow of instructions and data and performs the necessary manipulation of data

  • Primary storage (memory) is used to store information for immediate access by the CPU

  • Note that there are many levels of cache used in primary storage

  • Secondary storage devices (e.g., the hard drive, CD-ROM drives, tapes, etc.) provide permanent storage of large amounts of data, but are much slower than primary storage

  • Input and Output devices provided interfaces between the computer and the user

Secondary Storage

Primary Storage

Control Unit

Arithmetic Logic Unit

Central Processing Unit


Input Devices

Output Devices

Overview of a Computer - Data Representation

  • The first computers used vacuum tubes to hold data

  • Vacuum tubes have two states - ON and OFF

  • An ON state represents a 1

  • An OFF state represents a 0

  • Eight vacuum tubes strung together can represent an 8 digit string of 0s and 1s

  • Put another way, this string is an 8 digit binary (base 2) number

  • We use decimal (base 10) numbers in our daily life

  • A decimal number is a string of digits whose values are drawn from the set {0,1,2,3,4,5,6,7,8,9}

  • In general, a number system is simply a way of representing numbers

  • A number system has a base (the number of digits used in the number system)

  • C
    onsider a number in a base b number system:

  • The value of this number is:

  • A binary number has a base of 2 where the valid digits are 0 or 1

  • E.g., 1001 binary == 9 decimal (1*8 + 0*4 + 0*2 + 1)

  • An octal number has a base of 8 where the valid digits are 0 through 7

  • E.g., 031 octal == 25 decimal (3*8 + 1)

  • A decimal number has a base of 10 where the valid digits are 0 through 9

  • E.g., 2000 decimal == 2000 (Y2K bug ;-))

  • A hexadecimal number has a base of 16 where the valid digits are 0 through F, i.e. {0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F}

  • E.g., xABBA hex == 43962 decimal (10*4096 + 11*256 + 11*16 + 10)

Overview of a Computer - Data Representation (2)
Powers of 2




2048 2K




4096 4K




8192 8K




16,384 16K




32,768 32K




65,536 64K




131,072 128K




263,144 256K




524,288 512K




1,048,576 1M


1024 1K


2,097,152 2M

1 KILO = 2^10 = 1024

1 MEG = 2^20 = 1024*1024 = 1,048,576

1 GIGA = 2^30 = 1024*1024*1024 = 1,073,741,824

  • T
    o evaluate a binary number, say 101101, simply add up the corresponding powers of 2:

Overview of a Computer - Hexadecimal Numbers

  • A hexadecimal number is a string of hexadecimal digits

  • Digits A, B, C, D, E, F represent the numbers 10, 11, 12, 13, 14, and 15

  • Hexadecimal is popular in the computer field because it can be used to concisely represent a long string of binary digits

  • Consider a 16 digit binary number:


  • Break this up into groups of 4:

1011 0001 1100 0101

  • Convert each group of 4 into decimal:

11 1 12 3

  • Then convert each decimal number into hex:


  • And you now have the number: Baker 1 Charlie 3

Able = A = 10 = 1010

Baker = B = 11 = 1011

Charlie = C = 12 = 1100

Dog = D = 13 = 1101

Easy = E = 14 = 1110

Fox = F = 15 = 1111

  • By the same token, the HEX number 3F2C1596 represents the binary string:

0011 1111 0010 1110 0001 0101 1001 0110

Overview of a Computer - Primary Storage

  • Primary storage, also known as main memory or RAM (random access memory) is used to store information for immediate access by the Central Processing Unit (CPU)

  • Memory can be viewed as a series of memory cells with each cell having its own individual address

  • E.g., think of a bank of mailboxes at a post office

  • The information contained in a memory cell is called the contents of that cell

  • Memory cells can be used to store data, such as characters or numbers

  • Internally, of course, they are all numbers, but we can choose to interpret some numbers as characters

  • They can also be used to store program instructions

  • These are “special” numbers that are meaningful to a CPU!

  • The smallest unit of computer storage is a bit, as in binary digit

  • Most computers group bits together to form larger entities

  • E.g., 8 consecutive bits often form a byte and 32 consecutive bits often form a word

  • A word on an Intel 286 computer is 16 bits or 2 bytes

  • A word on an Intel 386, 486, and Pentium computers is 32 bits or 4 bytes

  • The next generation of Intel computers (e.g. the Merced) will use 64 bit words, i.e. 8 bytes

  • The DEC Alpha computer is currently using 64 bit words

  • Many mainframe computers, such as the Unisys A-Series, use 48 bit words

  • Memory cells in a computer are typically one byte or one word in size

  • A word is a unit of information that can be transferred to and from memory

  • A kilobyte of memory, as in 1K, is 1024 bytes of memory

  • A megabyte of memory, as in 1M, is 1024K of memory, or 2^20 bytes

  • A gigabyte of memory, as in 1G, is 1024M of memory, or 2^30 bytes

  • Note that a 32 bit word can represent 2^32 different possible values

Programming Languages - Low Level Languages

  • Computers only do what they are told to do

  • Except in Hollywood movies, e.g., 2001, Terminator 2, the Matrix, etc. ;-)

  • In order for a computer to perform a task, it must be given a series of specific instructions in a language it can understand

  • The fundamental language of any computer is its machine language

  • This is typically sequences of zeroes and ones

  • In the very early days of computers, this was the only way one could write programs!!!

  • To relieve the suffering of these early programmers, a higher level language called assembly language was developed

  • Assembly language contains mnemonic words and symbols for the binary machine instructions

  • An assembler maps assembly language instructions into machine language instructions

  • Assembly language programming is indeed a significant improvement over machine language programming

  • However, it has the following drawbacks:

  • Machine dependent - each computer architecture has its own unique assembly language

  • Low level instructions - writing programs is very time consuming, tedious, and error-prone

Programming Languages - High Level Languages

  • A general trend in computing over the past 4 decades is to elevate programming from low level to higher level languages

  • I.e., high level languages are geared more toward people writing the programs rather than the computer

  • Assembly language instructions map directly to machine instructions

  • High level language instructions must be translated/compiled into machine instructions

  • High level languages are more “problem-oriented” than assembly/machine languages

  • E.g, they require little or no knowledge of the underlying computer architecture

  • Learning how to write/debug programs in high level languages is much easier and less error-prone than learning how to write/debug equivalent programs in assembler

  • E.g., high level languages required fewer statements to do the same thing as assembler

  • Programs written in high level languages can be ported much more easily to different computer architectures

  • E.g., the compiler encapsulates the machine-dependent details of the target assembly language

  • A special program called a compiler is needed to translate a program written in a high level language into assembly code (which is then transformed into native machine code by an assembler)

  • The statement written in the high level language are called source code

  • The compiler/assembler's output is called object code

Language Taxonomy

History of C

Significant Points About C
· Small number of keywords

· Widely available, particularly on personal computers and workstations

· Can be used very portably

· Standard library

· Preprocessor may be used to isolate machine dependent code

· Unlike Pascal, which has many dialects

· Native language of UNIX (tm) and Windows NT

· Terse

· Powerful set of operators

· Statements can be very powerful

· Some are bit level operators

· Designed to be implemented efficiently on many machines

· Modular -- functions

· Parameters are typically passed `by value’

· No nested functions

· Syntax is complicated

· Semantics of certain features are complex and error-prone

A Comparison of Programming Language Philosophy
· Strict Parent (a “bondage and discipline” language ;-))

· Restricts programmer for his/her own good

· A white, automatic transmission automobile with lots of safety features (e.g., air bags, controls that limit speed to 55 miles per hour and prohibit leaving the lights on or locking the keys in the car)
· A permissive, easy going parent (a ‘lassize-faire’ language ;-))

· Assumes that the programmer knows what he/she is doing and will assume responsibility for his/her actions. (Some describe it as a “gun with which you can shoot yourself in the foot.”)

· A bright red ’65 Corvette with a big block engine, manual transmission, optional seat belt, and with fuzzy dice hanging from the rear view mirror.
· A less permissive, yet open minded parent (e.g., ‘Thomas Huxtable’ ;-))

· Assumes that the programmer generally knows what he/she is doing, but provides more checking by default. (“With C++ it’s harder to shoot yourself in the foot, but when you do, you’ll blow off both of your legs” – Bjarne Stroustrup)

· A bright red 2000 Corvette with a 6 speed manual transmission, air bag, and heads up display, many on board computers

Example C Program


File: hello.c

Description: Prints a greeting to stdout.

Author: Douglas C. Schmidt


int main (void) /* execution starts in main */


printf ("Hello world.\n");

return 0;


· All C programs must have a function in it called main

· Execution starts in function main

· C is case sensitive!

· Comments start with /* and end with */. Comments may span over many lines.

· C is a “free format” language.

· The #include statement instructs the C compiler to insert the entire contents of file stdio.h in its place and compile the resulting file.

Compiling a C Program
· On a personal computer using Visual Studio, you will create a .c file, e.g. hello.c (as in the previous example). You will then compile it to produce a .exe file (e.g., hello.exe) and perhaps a .obj file (hello.obj). Consult your compiler documentation (each one is different).

  • In Visual Studio, do a File|New and you will see the following dialog...

  • Here, you must first select Win32 Console Application. Then press the ... button that appears to the right of the Location

  • Now choose the location. You may need to create a folder on your file system. In this case, I brought up the Windows NT explorer and created the new folder Ece11-s98. Whatever you do, you should place the project in a place such that you can easily find it later.

  • Now that you have specified a Location, i.e. a folder where you want your project created, you should see the following...

  • Now, specify the name of your project. Visual Studio will create a folder underneath the one you specified for Location by that name. This will also become the name of your executable... Finally, click on the OK button to record your selection.

  • It is very important that you do each of these initial steps in the exact order that I have described above. That is, first specify that you want a Console Application, then specify the location, then specify the project name. Do not forget any of these steps. In other words, pay attention!!!

  • As a result, you will see the following in Visual Studio

  • N
    otice that the Workspace window now has three tabs. It has a ClassView tab, a FileView tab, and an InfoView tab. Select (point the mouse to) the FileView tab.

  • After selecting the FileView tab, you should see the following. Notice what appears in the Workspace window...

  • Now we need to create a source file and include it in the project. If we do the correct sequence of steps, Visual Studio will automatically include the new file into the project.

  • Do a File|New and select Text File and then specify a File name. Do not accept the default choice, Active Server Page (or whatever happens to be the default). Do not select C/C++ Header File. Do not select C++ Source File. Select Text File. Do not forget to type in the file name, i.e. hello.c (or whatever you wish to call it), but it must end with .c !!! The file suffix tells Visual Studio what type of file this is so it knows which compiler to invoke on it. Finally, click OK to select your choice.

  • As a result of your efforts, you should see the following.

  • I usually move the windows around at this point, adjusting the sizes.

  • Type in the program.

  • If you click on the + by Hello files under Workspace, you will see a list of all of the files in your project

  • B
    uild your program by selecting the Build|Build menu option

  • Run it (Build | Execute)

Now let's look at the files:

Hello.dsw: this is your WORKSPACE

Hello.dsp: this is the project build file

These two files, along with hello.c are worth saving.

  • The program we just built is HELLO.EXE under the Debug directory

  • Because it is a CONSOLE application, we can run it directly from our Windows NT command (or Windows 95 Dos) prompt.

  • When I typed hello below at the Dos prompt, Windows ran the program hello.exe. Below you can see the results of this run.

Compiling Under UNIX
To compile a C program under UNIX, one may do it in the following ways:
% cc hello.c
This compiles the file and creates an executable named a.out
% cc hello.c -o hello
This compiles the file but renames the executable hello
% cc -c hello.c
This compiles the file but does not link it, thus producing an object module which may be linked later on. That file, by default, is hello.o
% cc hello.o -o hello
This links the object file hello.o to create the executable hello
Under UNIX, suffixes are important (i.e., .c versus .o). They tell the compiler what type of file they are, i.e. a C program file versus an object module.
% cc foo.o bar.o -o fubar
This links two separately compiled modules into an executable named fubar.
The compiling process -- overview

Compiling process -- translation phases (ANSI)
1. Physical source file characters are mapped to the source character set (including new-line characters and end-of-file indicators) if necessary. Trigraph sequences are replaced by corresponding single-character internal representations.
2. Each instance of a new-line character and an immediately preceding backslash character (\) is deleted, splicing physical source lines to form logical source lines.
3. The source file is decomposed into preprocessing tokens and sequences of white-space characters (including comments). A source file shall not end in a partial preprocessing token or comment. Each comment is replaced by one space character. New-line characters are retained.
4. Preprocessing directives are executed and macro invocations are expanded. A #include preprocessing directive causes the named header or source file to be processed from phase 1 through phase 4 recursively.
5. Each source character set member and escape sequence in character constants and string literals is converted to a member of the execution character set.
6. Adjacent character string literal tokens are concatenated and adjacent wide string literal tokens are concatenated.
7. White-space characters separating tokens are no longer significant. Each preprocessing token is converted into a token. The resulting tokens are syntactically and semantically analyzed and translated.
8. All external object and function references are resolved. Library components are linked to satisfy external references to functions and objects not defined in the current translation. All such translation output is collected into a program image which contains information needed for execution in its execution environment.

Copyright (c) 1998 by Robert C. Carden IV, Ph.D.


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