working environment - ariel.ac.il ?· 2 working environment • linux, gcc • we’ll work with...

C
#include int main() {
printf ("hello class\n"); return 0;
}

2
Working environment
• Linux, gcc
• We’ll work with c9.io website, which works with
ubuntu
• I recommend to install ubuntu too
• Also in tirgul

History
3
70’s – Development of UNIX. (Richie+Kernigham – Bell labs)
80’s – Large efficient code. (Stroustrup – Bell labs)
90’s – Language for the web. (Sun Microsystems)
Simple to convert to
machine code. VM
Fast and Efficient Secure and Safe
Welcome to C Easy to avoid bugs
Easy to Debug
C++C Java

History – C:
K&R 1st
ed. ('78) ANSI C
('89) C99 ('99)
C11(’11)
This course, without the VLA!
• First "standard"
• Default int
•Enums
•Return struct
•void
• //
• VLA
• variadic
macros
•inlining
•multithreading
•Anonymous
structs
• _Generic

5
C – Design Decisions
“Bare bones” – the language leaves maximal flexibility
with the programmer
Efficient code (operating systems)
Full control on memory & CPU usage
High-level
Type checking
High-level constructs
Portable
Standard language definition
Standard library

C – Warning Signs
6
No run-time checks
Array boundary overruns
 Illegal pointers
No memory management
Programmer has to manage memory

First Program in C
7
// This line is a comment,
/* and this line also. */
// This line defines standard I/O library
#include
// main – program entry point. Start form here
int main()
{ // {…} define a block
printf("Hello class!\n");
return 0;
}
7

Similar to java – you should know it already.
8
The basic syntax

Basic
9
• Case sensitive
• White-space not important.
• End statements with “;”
• Code block defined with “{” and “}”
• Return value from function using “return X;”
• String with “ " ”
• All lines below are legal:
int x,y;
x=5; {
x; } ;

Statements - conditional
10
if (expression)
//statement or block
else if (expression)
else (expression)
switch (integer value)
later...

Statements - loops
11
The usual suspects:
int x,y; //in ANSI C you cannot declare inside
the for!
for (x=0,y=0;x

Statically typed – each variable has a type. Declare by:
.
int x;
int x,y;
Optionally initialize (otherwise undefined!)
int x=0;
Variables
12

int x;
Undefined value: as in this example, can have any T (here T=int) value.
Undefined behavior: Everything may happen. Probably
won’t format your disk, but may very well give a hacker a
way to do it…
The biggest problem: often programs seems to work
fine although their behavior is undefined, and then…
Undefined – important!
13

Variables
14
Where to declare?
1. Inside a block (C89 - block beginning) , will be visible only
in block.
2. Outside all blocks – global - will be visible everywhere.
int x=0; // global int main()
{ int x=1; //local hides global
{ int x=2; //local hides outer scope //x is 2
} //x is 1 again!
}

Scopes
15
• Code block defined with “{” and “}”.
• Only declarations inside current or outer scopes are visible.
• Declarations in inner scope hide declarations in outer
scopes:
• Outmost scope (global) had no brackets.
• Keep in mind that a function is also a scope.
int y=5,x=0; {
int x=y; //x is 5 {
int y; }
} // x is 0

Second Program
16
#include int main() {
int i; // declares i as an integer int j = 0; // declares j as an integer,
// and initializes it to 0 // for( initial ; test condition ; update step ) for( i = 0; i < 10; ++i ) {
j += i; // shorthand for j = j + i printf("%d %d %d\n", i, j, (i*(i+1))/2);
} return 0;
}
16

Running…
17
0 0 0
1 1 1
2 3 3
3 6 6
4 10 10
5 15 15
6 21 21
7 28 28
8 36 36
9 45 45
17

Functions
18
C allows to define functions
Syntax:
int power( int a, int b )
{
…
return 7;
}
Return type Parameter
declaration
Return
statement
18

Procedures
19
Functions that return void
void power( int a, int b )
{
…
return;
}
Return w/o value
(optional)
19

Example – printing powers
20
#include
int power( int base, int n )
{
int i, p;
p = 1;
for( i = 0; i < n; i++ )
{
p = p * base;
}
return p;
}
int main()
{
int i;
for( i = 0; i < 10; i++ )
{
printf("%d %d %d\n",
i,
power(2,i),
power(-3,i) );
}
return 0;
} 20

Functions Declaration
21
“Rule 1”: A function
“knows” only
functions which were
declared above it.
void funcA()
{
...
}
void funcB()
{
funcA();
}
void funcC()
{
funcB();
funcA();
funcB();
}
void funcA()
{
...
}
void funcB()
{
funcC();
}
void funcC()
{
funcB();
}
Error:
funcC is not
known yet.
21

Functions Declaration
void funcC(int param);
// or: void funcC(int);
void funcA()
{
}
void funcB()
{
funcC(7);
}
void funcC(int param)
{
}
Amendment to “Rule 1” : Use forward declarations.
22

Boolean variables – non!
23
int main()
{
int a = 5;
while(1)
{
if(!(a-3))
{
printf("** a=3 **\n");
break;
}
printf("a=%d\n",a--);
}
return 0;
}

24
Building a program in C:
Preprocessor, Compilation and Linkage

Building a program in C – Preprocessor
25
A text processor
Commands start with #
// copy & paste the file here
#include
hello.c
Preprocessor
stdio.h
tmpXQ.i
(C code)

Building a program in C – Compiling
26
Takes input C-code and produces machine code (object
file)
The object file does not contain all external references: It
leaves names, such as “printf”, “area”, etc. as undefined
references
hello.c
Preprocessor Compiler
stdio.h
tmpXQ.i
(C code)
hello.o
(object
file)

Linking
27
Combines object file with external references into an
fully executable file, with no unresolved references
Main
Preprocessor,
Compiler
Main.c Main.o
Linker
libc.a

Link errors
28
Gcc: /media/sf_BitEagle_Projects/cbitcoin/test/testC BAddress.c:40: undefined reference to `CBNewByteArrayFromString‘
Visual studio: Error 1 error LNK2019: unresolved external symbol _foo referenced in function _main
c:\Users\ofirpele\documents\visual studio 2012\Projects\ConsoleApplication5\ConsoleAp plication5\ConsoleApplication5.obj
ConsoleApplication5

29
The Preprocessor

Compilation in C
30
hello.c
Preprocessor Compiler
stdio.h
tmpXQ.i
(C code)
hello.o
(object
file)

Preprocessor
31
A single-pass program that:
1. Include header files
2. Expands macros
3. Control conditional compilation
4. Remove comments
Outputs – a code ready for the
compiler to work on.

Preprocessor
32
In linux with gcc, we can test what
the preprocessor does:
> gcc –E hello.c
will print the C code after running the
preprocessing

#include directive
33

working environment - ariel.ac.il ?· 2 working environment • linux, gcc • we’ll work with...

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