1. C #include <stdio.h> 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

3. History C C++ Java VM Simple to convert to machine code.
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) VM
Simple to convert to
machine code.
Fast and Efficient
Secure and Safe
Welcome to C
Easy to avoid bugs
Easy to Debug

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

5. C – Design Decisions Efficient code (operating systems)
“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

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

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

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

9. Basic 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; } ;

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

11. Statements - loops
The usual suspects: int x,y; //in ANSI C you cannot declare inside the for! for (x=0,y=0;x<10 && y<5;x++,x+=2) //statement or block while (condition) //statement or block do //statement or block while (condition)

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

13. Undefined – important!
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…

14. Variables Where to declare?
Inside a block (C89 - block beginning) , will be visible only in block.
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 }    //x is 1 again! }

15. Scopes int y=5,x=0; { int x=y; //x is 5 { int y; } } // x is 0
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 {       int y;    } } // x is 0

16. Second Program
#include <stdio.h> 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

17. Running… 17

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

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

20. Example – printing powers
#include <stdio.h> 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

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

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

23. Boolean variables – non!
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

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

26. Building a program in C – Compiling
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)

27. Linking
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
Actually a library (.a) is just a collection of object (.o) files chained together to one file.
Compiling and linking can be combined into one command (supply the c file as an input, and use –o to specify executable) some libraries are implicitly linked. (libc.a) others (e.g. math = libm.a) – need to use -l<lib name> where in linux the lib prefix and .a suffix can be omitted.

28. Link errors
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

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

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

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

33. #include directive
#include  "foo.h" Include the file “foo.h”, from current directory
#include <stdio.h> Include the file “stdio.h” from the standard library directory (part of compiler installation)

34. Modules & Header files Square.h Square.c Main.c
// interface of function
int area     (int x1,int y1, int x2, int y2); ...
Complex.c
Square.c
#include "Square.h" int main() {    area (2,3, 5,6); }
Main.c
#include "Square.h"  #include <math.h> // implementation int area (int x1,int y1,int x2, int y2) {
... }

35. Do all files get compiled every time we build the program???
$ gcc –c Square.c –o Square.o
$ gcc –c Main.c –o Main.o
$ gcc Square.o Main.o –o Main
Main
Preprocessor
Compiler
Square.c
Square.o
Main.c
Main.o
Linker
libc.a

36. Definition of data types Declarations of functions & constants
Header files
Header file contain
Definition of data types
Declarations of functions & constants
That are shared by multiple modules.
#include directive allows several modules to share the same set of definitions/declarations

37. is equivalent to #define directive #define FOO 1 int x = FOO;

38. #define with arguments
#define SQUARE(x) x*x b = SQUARE (a);
is the same as
b = a*a;

39. #define – cautions Is it what we intended?
#define SQUARE (x) x*x b = SQUARE (a+1); c = SQUARE (a++);
Is it what we intended?
b = a+1*a+1; //Actually: b = 2*a+1; c = a++*a++; //Actually: c = a*a; a+=2;

40. #define – cautions Is it what we intended?
#define SQUARE (x) ((x)*(x)) b = SQUARE (a+1); c = SQUARE (a++);
Is it what we intended?
b = ((a+1)*((a+1)); //Now ok c =  ((a++)*(a++)); //Did not help: c = a*a; a+=2;

41. #define directive should be used with caution!
Alternative to macros:
Constants
enum { FOO = 1 }; or
const int FOO = 1;
Functions – inline functions (C99,C++)

42. #define
Multi-line: All preprocessor directive effect one line (not c statement). To insert a line-break, use “\”: BAD: #define x (5 + 5) // x == 10 ! GOOD: #define x (5 + \ 5)

43. Allows to have conditional compilation
#if directive
Allows to have conditional compilation
#if defined(DEBUG) // compiled only when DEBUG exists printf("X = %d\n", X); #endif

44. #ifndef – for header safety
Complex.h:
struct Complex {
...      MyStuff.h:
#include "Complex.h"
Main.c:
#include "MyStuff.h" #include "Complex.h"
Only one definition is allowed!
Error:
Complex.h:1: redefinition of `struct Complex'

45. #ifndef – header safety
Complex.h (revised):
#ifndef COMPLEX_H #define COMPLEX_H struct Complex { ...
#endif Main.c:
#include "MyStuff.h" #include "Complex.h" // no error this time

46. #pragma once – header safety
Complex.h (revised):
#pragma once struct Complex { ...
Main.c:
#include "MyStuff.h" #include "Complex.h" // no error this time

47. Preprocessor – summary
Text processing program.
Does not know c rules
Operates before compilation, output passed to compiler.
Can do copy and paste / cut
#include paste the included file here Commonly included file (.h by convention) contains forward declarations
#define copy the macro body, paste it where macro name appears - constants, simple "functions"
#if condition not fulfilled, cut the code - Conditional compilation – e.g. debugging code
Note – in order to be able to compile, the compiler must know about the existence of a function before it is used. It does not need to know the exact implementation - it can leave it as a name, and let the linker insert the actual jump address, but it must know it's declaration.

48. Debug/Test mode vs Release mode

49. Debug/Test mode vs Release mode
#include <assert.h> #define MAX_INTS 100 int main() { int ints[MAX_INTS]; // i should be in bounds, but is it really? i = foo(<something complicated>); // safety assertions assert(i>=0); assert(i<MAX_INTS); ints[i] = 0; ...

50. Debug/Test mode vs Release mode
#include <assert.h> #define MAX_INTS 100 int main() { int ints[MAX_INTS]; // i should be in bounds, but is it really? i = foo(<something complicated>); // safety assertions assert(i>=0); assert(i<MAX_INTS); ints[i] = 0; ...

51. #define NDEBUG
#include <assert.h> #define MAX_INTS 100 int main() { int ints[MAX_INTS]; // i should be in bounds, but is it really? i = foo(<something complicated>); // safety assertions assert(i>=0); assert(i<MAX_INTS); ints[i] = 0; ...

52. assert // bad, foo() will not be called
// if the compiler removes the assert() 
// if NDEBUG is defined
assert(foo() == 0);
// good
int errCode = foo();
assert(errCode == 0);

53. assert Use for: Catching bugs Don't use for:
checking malloc, user input,...

54. assert.h
#include <assert.h> // Sqrt(x) - compute square root of x // Assumption: x  non-negative double sqrt(double x ) {    assert( x >= 0 );  // aborts if x < 0 …

55. assert.h
// procedure that actually prints error message void __assert(char* file,int line,char* test);
#ifdef NDEBUG #define assert(e)     ((void)0) #else #define assert(e) \
((e) ? (void)0 : \ __assert(__FILE__, __LINE__, #e)) #endif

56. assert.h
Important coding practice
Declare implicit assumptions
Sanity checks in code
Check for violations during debugging/testing

57. Compilation

58. Compilation Translate the c code to machine code.
Every machine architecture has a different code. Need separate compilation.
x86 : older but still common PCs “32-bit” (Intel/AMD)
x64 : newer PCs “64-bit” (Intel/AMD)
ARM : (many versions) Phones, tablets (ARM)
Translated code is an “executable” – the OS can load it to the machine memory, and the let the CPU do whatever you wrote in the code.

59. “Assembly”
int y=2; int mult(int x) { return x*y; mov eax,dword ptr [x] imul eax,dword ptr [ h] } int main() { return mult(5); push 5 call 11711A4h } Only part of the assembly code is shown here. Actually each command has binary code, and the sequence of these code is the object file.

60. Compiling warnings

61. Compiling warnings Add “-Wall” flag to catch things like this:
if (i=3) { //bug, we meant i==3 … }