CS 262
George Mason University
Department of Computer Science
Syllabus
www.hamzamughal.com
Also available on the course blackboard page
Why learn C?
C is dominating Microcontroller and Embedded systems programming
A brief introduction to C
Lets take a trip down memory lane!
Where?
in the Computer Science Research Department of Bell Labs in Murray Hill, NJ
Who?
by Dennis Ritchie
Why?
Previous languages (such as B) were difficult to implement programs in due to
various issues such as hardware constraints and B being incredibly slow due to it being
an interpreted language (executed by software running on top of the CPU)
C was developed to move code from assembly to a “higher” language, being
tied to the development of Unix to provide more control
https://www.bell-labs.com/usr/dmr/www/chist.pdf
PDP 11
ANSI (American National Standards Institute) standardized C in 1989 to create ANSI C
The International standard (ISO) was adopted by ANSI in 1990 which is known as C89
Updates in 1995 (C05) and 1999 (C99), latest being in 2018 (C18)
More on C
C is a “medium level” programming language that lets us use it at a “low level”
Contains the usual structures that many “high level” languages offer to us but also
allowing us directly access memory and hardware
Numerous library functions available that may be imported
C is a Compiled, Imperative, and Statically Typed Language
Pitfalls
Easy to write spaghetti code since C is procedural
Preprocessors can get messy quick
Unable to gracefully terminate (meaning no catch/throw/exceptions!)
Not much of OOP
Quite an unsafe language
Many more which I’ve not included here…
White House Memorandum circa
February 2024
https://www.whitehouse.gov/wp-content/uploads/2024/02/Final-ONCD-TechnicalReport.pdf
“BACK TO THE BUILDING BLOCKS: A PATH TOWARD SECURE AND MEASURABLE
SOFTWARE”
“Programmers writing lines of code do not do so without consequence…This
report explores how such metrics can shift market forces to improve cybersecurity
quality across the ecosystem.”
“Experts have identified a few programming languages that both lack traits associated
with memory safety and also have high proliferation across critical systems, such as C
and C++.”
“According to experts, both memory safe and memory unsafe programming
languages meet these requirements. At this time, the most widely used languages that
meet all three properties are C and C++, which are not memory safe programming
languages.”
“Through the adoption of memory safe programming languages, creators of software
and hardware can better secure the building blocks of cyberspace and proactively
eliminate entire classes of bugs
Crowdstrike
Crowdstrike released an “analysis” on their crash that occurred on July 19th:
https://www.crowdstrike.com/wp-content/uploads/2024/08/Channel-File-291Incident-Root-Cause-Analysis-08.06.2024.pdf
“The Rapid Response Content for Channel File 291 instructed the Content Interpreter to
read the 21st entry of the input pointer array. However, the IPC Template Type only
generates 20 inputs. As a result, once Rapid Response Content was delivered that used a
non-wildcard matching criterion for the 21st input, the Content Interpreter performed
an out-of-bounds read of the input array”
Structure of a C Program
Consists of one or more functions (not methods as they are called in Java)
Program consists of executing the main function (entry point of your program)
int main () { … }
int main (int argc, char *argv[]) { … }
Functions contain:
A heading (data type return, name, optional arguments)
Argument declarations (if any optional arguments)
Statements (code inside the curly braces)
Preprocessors (macros, compiler controls, constant values, libraries, etc)
Additional local and external functions and variables
Recall control returns to the place where a function was called (may or may not return
with a value)
Statements must end with a semicolon (same as Java)
Compound instructions must be enclosed with curly braces { … }
Comments delimited by // or by multi line comments /* */
Layout of a C File
Hello World in C….
Brief intro to language processing systems
Source Code
4 Steps of compilation
Pre processer
.i file
Compiler
.s file
Assembler
.o file
Linker
.exe file
Source Code
4 Steps of compilation
Pre processer
.i file
1. Removes all
comments
2. Expands out
macros in code
with the
corresponding
macro value
3. Pulls in any
included header
files into the
source file
Compiler
.s file
1. Transforms
output of the pre
processing steps
into assembly
code
Assembler
.o file
1. Transforms
assembly code
into binary byte
code
1. Links together all
the byte code (.o
or object files) to
product an
executable that
can be ran
Linker
.exe file
GCC
GNU Compiler Collection (aka gcc)
optimizing compiler which we will use to compile our c code
How do we utilize gcc exactly?
gcc –o hello hello.c
This command basically says compile “hello.c” to machine code executable named
hello
The executable “hello” is now created, now how do we run it?
./hello
Executes hello
./ is necessary (./ specifies the directory you’re in currently)
Connecting to Zeus
Off campus? First connect to the VPN
Download the Cisco VPN https://its.gmu.edu/service/virtual-private-network-
vpn/
Connecting by SSH to Zeus via command line
ssh username@zeus.cec.gmu.edu
Once connected to Zeus, the Bash Shell waits for input
A command line interpreter which runs commands, programs, shell scripts
bash being the standard shell and the $ character being its default prompt
Some commands which you may utilize the most within the bash shell:
clear
man
pwd
ls
cd
cp
mv
rm
mkdir rmdir cat
Copying files from/to Zeus
From your computer to Zeus (in a terminal not connected to Zeus)
scp local_path/file_name user@zeus.cec.gmu.edu:~/remote_path
From Zeus to your computer (in a terminal not connected to Zeus)
scp user@zeus.cec.gmu.edu:~/remote_path/file_name local_path
Vi/Vim
We will utilize vi/vim on Zeus
Text editor to create/edit files
Two modes:
Command mode and Insert Mode
Command mode to insert mode – type i
Insert mode to command mode – hit the escape key
Some commands which you may find useful:
vim filename (create a file named filename or edit existing file if it exists)
:wq (write file and exit)
:q (Quits, warning is printed if current file is not saved prior)
:q! (Quits with no warning)
:w (Save file)
Java and C Comparisons
Java runs on the JVM, provides a safe programming environment by allowing stuff
such as array bounds checks
C runs on the machine directly which does not contain such sanity checks that Java
has
Java
Portable
Efficient
Safe
C
Java
C
Portable
True
False
Efficient
False
True
Safe
True
False
Java
Strings
C
Strings
Java
C
String s = “Hello”;
char s2[6] = “Hello”;
Strings
String Concatenation
Java
C
String s = “Hello”;
char s2[6] = “Hello”;
Java
C
Strings
String s = “Hello”;
char s2[6] = “Hello”;
String Concatenation
s1 + s2
#include <string.h>
strcat(s1,s2)
Java
C
Strings
String s = “Hello”;
char s2[6] = “Hello”;
String Concatenation
s1 + s2
#include <string.h>
strcat(s1,s2)
Arrays
Java
C
Strings
String s = “Hello”;
char s2[6] = “Hello”;
String Concatenation
s1 + s2
#include <string.h>
strcat(s1,s2)
Arrays
Int [] x = new int[10];
Int x[10];
Java
C
Strings
String s = “Hello”;
char * s = “Hello”;
char s2[6];
strcpy(s2, “Hello”)
String Concatenation
s1 + s2
#include <string.h>
strcat(s1,s2)
Arrays
Int [] x = new int[10];
Int x[10];
Pointers
Java
C
Strings
String s = “Hello”;
char * s = “Hello”;
char s2[6];
strcpy(s2, “Hello”)
String Concatenation
s1 + s2
#include <string.h>
strcat(s1,s2)
Arrays
Int [] x = new int[10];
Int x[10];
Pointers
Objects are implicit pointers
Int *p
Operators (nearly identical!)
arithmetic: +, -, *, /, %
assignment: =
augmented assignment: +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=
bitwise logic: ~, &, |, ^
bitwise shifts: <<, >>
boolean logic: !, &&, ||
equality testing: ==, !=
subexpression grouping: ()
order relations: <, <=, >, >=
increment and decrement: ++ and -member selection: ., ->
Slightly different than Java because there are both structures and pointers to
structures, more later
conditional evaluation: ? :
Fundamentals
Declarations
All variables need to be declared with a
type before use
If a local variable has no initialization,
it will contain garbage!
Basic syntax to create a variable:
data type var_name;
C17/18 ISO Standards: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2310.pdf
Variable naming
Consist of letters and/or digits. They should not be key words, they can’t contain
special symbols, such as blanks, -, ", etc.
A few C Keywords
typedef, return, for, char, if, goto, …
The first character must be a letter or the symbol (_)
An uppercase letter is not equivalent to a lowercase
Data Types
char – Character (1 byte)
Int – Integer
float – Floating point numbers
double – Floating point with double precision
These data type may be coupled with the words – unsigned, signed, short, and long
before the data type
The byte size assigned to the data type usually depends on the capacity of the
computer and the compiler used (i.e. system dependent). However, a char is always 1
byte regardless of the system.
Constants
Like variables, except their values never change
Also known as literals, need to specify the data type of the constant
Common practice to define constants in UPPER-CASE
const data_type constant_name;
Macros
Line of code defined near the top of a file using the #define keyword with the syntax
being as follows (note there is no semicolon at the end of the value):
#define name value
#define PI 3.14
Once we define a macro, we can use it in our code where all macro names are
replaced with the corresponding macro value
What would happen
to PI if we were to
compile our code?
Printing formatted input
printf(format string, …); // need to include stdio.h to use printf
If you have worked with System.out.printf in Java, then C’s printf is similar!
The format string uses Conversion Characters for values (see next slide)
printf(“The speed is %d miles per hour.\n”, speed);
Placeholders can also specify widths and precisions
%10d : add spaces to take up at least 10 characters
%010d : add zeros to take up at least 10 characters
%.2f : print only 2 digits after decimal point
%5.2f : print 1 decimal digit, add spaces to take up 5 chars
Format Specifiers
To indicate a data type, the sign % is placed before the conversion character
The Ascii Table
Character variables
in C contain ASCII values
decimal values between 0-127
Rather than using the ASCII value,
simply use its character value instead
i.e. char c = ‘A’;
Escape sequences
Exercises
Compute the circumference and area of a circle with a given radius. Choose any value
for the radius.
Tasks this week
Familiarize yourself with a text editor (either Vim or Visual Studio, etc)
Learn to work with Unix commands
Lab 1
Working with Zeus
“All theory and no practice makes Jack a dull boy”