Introduction to C Programming

Copyright Copyright © 2011 to author(s). All rights reserved All content in this presentation, including charts, data, artwork and logos (from here on, "the Content"), is the property of Amr Ali or the corresponding owners, depending on the circumstances of publication, and is protected by national and international copyright laws. Authors are not personally liable for your usage of the Content that entailed casual or indirect destruction of anything or actions entailed to information profit loss or other losses. Users are granted to access, display, download and print portions of this presentation, solely for their own personal non-commercial use, provided that all proprietary notices are kept intact. Product names and trademarks mentioned in this presentation belong to their respective owners. Amr Ali Abdel-Naby@2011 Introduction to C Programming 2

Course Objective After completing this course, you will be able to: Write programs in C language Understand what are the constructs of the C language Implement data structures and algorithms in C Amr Ali Abdel-Naby@2011 Introduction to C Programming 3

Course Notes Set your cell phone to vibrate. I assume you know computer architecture. Ask any time. During labs, feel free to: Check any material Search internet Amr Ali Abdel-Naby@2011 Introduction to C Programming 4

Course References www.cprogramming.com C by Example www.opengroup.com http://ocw.mit.edu/index.htm Amr Ali Abdel-Naby@2011 Introduction to C Programming 5

Outline Introduction to C Variables and Data Types Blocks and Compound Statements Control Flow Modular Programming Variable Scope I/O Pointers and Memory Addresses Arrays and Pointers Arithmetic Search and Sorting Algorithms User Defined Data Types Data Structures Callbacks Hash Tables Using External Libraries Creating Libraries Standard Library Amr Ali Abdel-Naby@2011 Introduction to C Programming 6

What is C? Invented by Dennis Ritchie – AT&T Bell Labs 1972 Widely used today Extends to newer system architectures Efficiency/performance Low-level access Amr Ali Abdel-Naby@2011 Introduction to C Programming 8

C Features Few keywords Structures, unions, compound data types.. Pointers, arrays… Standard library Compiles to native code Macro preprocessor Amr Ali Abdel-Naby@2011 Introduction to C Programming 9

C Evolution 1972 – C Invention 1978 – 1st specification published 1989 – C89 standard (ANSI C or standard C) 1990 – ANSI C adopted by ISO, AKA C90 1999 – C99 standard Not completely implemented in many compilers 2007 – Work on new standard C1X announced We will focus on ANSI/ISO C (C89/C90) Amr Ali Abdel-Naby@2011 Introduction to C Programming 10

C Usage Systems programming Operating systems Microcontrollers Embedded processors DSP processors Amr Ali Abdel-Naby@2011 Introduction to C Programming 11

C vs. Others Recent derivatives: C++, C#, Objective-C Had an effect on: Java, Perl, Python C lacks: Exceptions Range checking Garbage collection OOP … Lower level language Amr Ali Abdel-Naby@2011 Introduction to C Programming 12

Editing C Code *.c extension for C source files *.h extension for C header files They are editable by any text editor. Amr Ali Abdel-Naby@2011 Introduction to C Programming 13

IDE – All in One Solution Examples: Eclipse CDT MS VC++ express edition KDevelop Xcode Compiler, editor, debugger… Suitable for large programs Amr Ali Abdel-Naby@2011 Introduction to C Programming 14

Structure of a C File Amr Ali Abdel-Naby@2011 Introduction to C Programming 15

Comments Ignored by the compiler Can appear anywhere Amr Ali Abdel-Naby@2011 Introduction to C Programming 16

The #include Macro A header file has constants, functions, and other declarations. #include reads the contents of the header file #include <header-file> searches for the header file in the include paths #include “header-file” searches for the header file in the current directory where the file it included it is in Amr Ali Abdel-Naby@2011 Introduction to C Programming 17

Declaring variables Must declare variables before use General form: type variable_name [=initial_value][,][…]; Uninitialized, variable assumes a default value Can declare/initialize multiple variables at once Amr Ali Abdel-Naby@2011 Introduction to C Programming 18

Arithmetic Expressions Amr Ali Abdel-Naby@2011 Introduction to C Programming 19

Order of Operations Orders of Operation Use parentheses to override order of evaluation Amr Ali Abdel-Naby@2011 Introduction to C Programming 20

Function Prototypes Functions also must be declared before use Declaration called function prototype Prototypes for many common functions in header files for C Standard Library General form: return_type function_name(arg1, arg2, …) Amr Ali Abdel-Naby@2011 Introduction to C Programming 21

The main() Function C Program entry point Can be one of: Amr Ali Abdel-Naby@2011 Introduction to C Programming 22

Function Definition Must match prototype (if there is one) Variable names don’t have to match Curly braces define a block Variables declared in a block exist only in that block Variable declarations must be before any other statements Amr Ali Abdel-Naby@2011 Introduction to C Programming 23

Our First Program Amr Ali Abdel-Naby@2011 Introduction to C Programming 24

More About Strings Strings stored as character array Null-terminated Last character in array is ‘’ Not written explicitly in string literals Special characters specified using escape character): - backslash, - apostrophe, - quotation mark , , , - backspace, tab, carriage return, linefeed oo, hh - octal and hexadecimal ASCII character codes 41 – ’A’, 60 – ’0’ Amr Ali Abdel-Naby@2011 Introduction to C Programming 25

Console IO stdout, stdin: console output and input streams puts(string): print string to stdout putchar(char): print character to stdout char = getchar(): return character from stdin string = gets(string): read line from stdin into string Amr Ali Abdel-Naby@2011 Introduction to C Programming 26

Preprocessor Macros They begin with #. They can take arguments. Parentheses ensure order of operations. Compiler performs inline replacement. Amr Ali Abdel-Naby@2011 Introduction to C Programming 27

Conditional Preprocessor Macros They can control which lines are compiled. Evaluated before code itself is compiled, so conditions must be preprocessor defines or literals Used in header files to ensure declarations happen only once Amr Ali Abdel-Naby@2011 Introduction to C Programming 28

Extra Preprocessor Macros Preprocessor directive Trigger a custom compiler error/warning message Remove the definition of a previously defined constant Amr Ali Abdel-Naby@2011 Introduction to C Programming 29

Definitions Datatype Determines the set of values an object can have and what operations that can be performed on it Operator Specifies how an object can be manipulated Expression Combination of values, variables, operators, and functions Variable Named link/reference to a value stored in the system’s memory or an expression that can be evaluated Amr Ali Abdel-Naby@2011 Introduction to C Programming 31

Variables Naming Rules Can contain letters, digits and _ Should start with letters Keywords (e.g., for,while etc.) cannot be used as variable names. Names are case sensitive. X is not as x. Amr Ali Abdel-Naby@2011 Introduction to C Programming 32

Data Types C has a small family of datatypes. Numeric (int, float, double) Character (char) User defined (struct, union) Numeric datatypes Amr Ali Abdel-Naby@2011 Introduction to C Programming 33

Variables Sizes and Endianess Sizes are machine/compiler dependent. sizeof(char) < sizeof(short) <= sizeof(int) <= sizeof(long) sizeof(char) < sizeof(short) <= sizeof(float) <= sizeof(double) For datatypes spanning multiple bytes, the order of arrangement of the individual bytes is important. Big endian vs. little endian Amr Ali Abdel-Naby@2011 Introduction to C Programming 34

Big Endian vs. Little Endian Amr Ali Abdel-Naby@2011 Introduction to C Programming 35

Constants Literal/fixed values assigned to variables or used directly in expressions Integers 3, 3UL, 0x12, 012 Floating point 3.141, 3.141F Character ‘A’, ‘41’, ‘101’ String “Hello world”, “Hello” “world” Enumeration enum bool{YES, NO}, enum color{R=1, G, B, Y=10} Amr Ali Abdel-Naby@2011 Introduction to C Programming 36

Operators Arithmetic +, -, *, /, % Relational >, >=, <, <=, ==, != Logical &&, ||, ! Increment and decrement X++, Y— --X, ++X Bitwise &, |, ^, ~, >>, << Assignment +=, &=… Amr Ali Abdel-Naby@2011 Introduction to C Programming 37

Conditional Expression Amr Ali Abdel-Naby@2011 Introduction to C Programming 38

Type Conversions C is a weakly typed language. It allows implicit conversions as well as forced casting. When variables are promoted to higher precision, data is preserved. char  int int  float As a rule (with exceptions), the compiler promotes each term in an binary expression to the highest precision operand. Amr Ali Abdel-Naby@2011 Introduction to C Programming 39

Blocks and Compound Statements Curly braces {} combine statements into a compound statement/block A block substitute a simple statement and compiled as a single unit. Variables can be declared in a block. A block can be empty or nested. Amr Ali Abdel-Naby@2011 Introduction to C Programming 41

Examples Amr Ali Abdel-Naby@2011 Introduction to C Programming 42

Booleans in C No booleans in C True is any non-zero value/result of a condition/expression. False is any zero value/result of a condition/expression. Expression must be numeric or a pointer. Amr Ali Abdel-Naby@2011 Introduction to C Programming 44

The if Statement Amr Ali Abdel-Naby@2011 Introduction to C Programming 45

The switch Statement Amr Ali Abdel-Naby@2011 Introduction to C Programming 46

The while Loop Amr Ali Abdel-Naby@2011 Introduction to C Programming 47

The for Loop Amr Ali Abdel-Naby@2011 Introduction to C Programming 48

The do-while Loop Amr Ali Abdel-Naby@2011 Introduction to C Programming 49

The break and continue Keywords break exists the innermost loop or switch statement. continue skips rest of innermost loop body, jumping to loop condition . Amr Ali Abdel-Naby@2011 Introduction to C Programming 50

goto Keyword Allows you to jump unconditionally to arbitrary part of your code (within the same function) The location is identified using a label. A label is a named location in the code. It has the same form as a variable followed by a ’:’ . Do not use it. Amr Ali Abdel-Naby@2011 Introduction to C Programming 51

Divide and Conquer Let’s design a program to solve linear Diophantine equation. ax + by = c where a, b, c, x, y are integers get a, b, c from command line compute g = gcd(a,b) if (c is not a multiple of the gcd) no solutions exist; Run Extended Euclidean algorithm on a, b rescale x and y output by (c/g) print solution Extended Euclidean algorithm: finds integers x, y s.t. ax + by = gcd(a, b). Amr Ali Abdel-Naby@2011 Introduction to C Programming 53

Returning Multiple Values Extended Euclidean algorithm returns gcd, and two other state variables, x and y Functions only return (up to) one value Solution: Use global variables Declare variables for other outputs outside the function. Variables declared outside of a function block are global. Persist throughout life of program Can be accessed/modified in any function Amr Ali Abdel-Naby@2011 Introduction to C Programming 54

In General Break down problem into simpler sub-problems. Consider iteration and recursion. Writing pseudocode first can help. Amr Ali Abdel-Naby@2011 Introduction to C Programming 55

Programming Modules in C C programs do not need to be monolithic. Module: interface and implementation Interface: header files Implementation: auxiliary source/object files Same concept carries over to external libraries. Lets take the extended Euclid as an example. Amr Ali Abdel-Naby@2011 Introduction to C Programming 56

ecluid.c Amr Ali Abdel-Naby@2011 Introduction to C Programming 57

ecluid.h Amr Ali Abdel-Naby@2011 Introduction to C Programming 58

Using Euclid Module Amr Ali Abdel-Naby@2011 Introduction to C Programming 59

Variable Scope The region in which a variable is valid. Many cases, corresponds to block with variable’s declaration Variables declared outside of a function have global scope Function definitions also have scope Amr Ali Abdel-Naby@2011 Introduction to C Programming 61

Scope and Nested Declarations Amr Ali Abdel-Naby@2011 Introduction to C Programming 62

Static Variables static keyword has two meanings, depending on where the static variable is declared Outside a function, static variables/functions only visible within that file Not global (cannot be extern’ed) Inside a function, static variables are local to that function Initialized only during program initialization Do not get reinitialized with each function call Amr Ali Abdel-Naby@2011 Introduction to C Programming 63

Register Variables During execution, data are processed in registers. Explicitly store commonly used data in registers Minimize load/store overhead Can explicitly declare certain variables as registers using register keyword Must be a simple type Only local variables and function arguments eligible excess/unallowed register declarations ignored, Registers do not reside in addressed memory Pointer of a register variable illegal Amr Ali Abdel-Naby@2011 Introduction to C Programming 64

Preliminaries IO facilities are provided by the standard library <stdio.h> and not by the language itself. A text stream consists of a series of lines ending with ’’. The standard library takes care of conversion from ’’−’’ . A binary stream consists of a series of raw bytes. The streams provided by standard library are buffered. Amr Ali Abdel-Naby@2011 Introduction to C Programming 66

Standard IO Amr Ali Abdel-Naby@2011 Introduction to C Programming 67

Formatted Output: printf It takes in a variable number of arguments. It returns the number of characters printed. The format can contain literal strings as well as format specifiers (starts with %). Amr Ali Abdel-Naby@2011 Introduction to C Programming 68

printf Format Specification - type %[flags][width][. precision][length]<type> Amr Ali Abdel-Naby@2011 Introduction to C Programming 69

printf Format Specification - width %[flags][width][. precision][length]<type> Amr Ali Abdel-Naby@2011 Introduction to C Programming 70

printf Format Specification - flag %[flags][width][. precision][length]<type> Amr Ali Abdel-Naby@2011 Introduction to C Programming 71

printf Format Specification - precision %[flags][width][. precision][length]<type> Amr Ali Abdel-Naby@2011 Introduction to C Programming 72

printf Format Specification - modifier %[flags][width][. precision][length]<type> Amr Ali Abdel-Naby@2011 Introduction to C Programming 73

Character Arrays Strings are represented as an array of characters. C does not restrict the length of the string. The end of the string is specified using 0. “hello”  {‘h’, ‘e’, ‘l’, ‘l’, ‘o’, ‘’} Amr Ali Abdel-Naby@2011 Introduction to C Programming 74

Comparing Strings strcmp in string.h compares two strings in dictionary order. Lower case letters come after capital case. ‘a’ > ‘A’ The function returns a value <0 if s comes before t The function return a value 0 if s is the same as t The function return a value >0 if s comes after t Amr Ali Abdel-Naby@2011 Introduction to C Programming 75

Formatted Input scanf reads characters from standard input, interpreting them according to format specification Similar to printf , scanf also takes variable number of arguments. Arguments have to be address of variables. The format specification is the same as that for printf . When multiple items are to be read, each item is assumed to be separated by white space. scanf ignores white spaces. It returns the number of items read or EOF. Amr Ali Abdel-Naby@2011 Introduction to C Programming 76

String IO Formatted data can be written to or read from character arrays. Amr Ali Abdel-Naby@2011 Introduction to C Programming 77

File IO C allows us to read/write data from text/binary files. We can: Open a file Close a file Read a single character Read a single line Write a single character Write a single line Read formatted line Write formatted line Amr Ali Abdel-Naby@2011 Introduction to C Programming 78

Project I: Game of Life Amr Ali Abdel-Naby@2011 Introduction to C Programming 79 Required: In lab-01.pdf, solve all problems. Duration: 120 minutes

Physical vs. Virtual Memory Physical memories are physical resources where data can be stored. Caches RAMs Hard disks Removable storage Virtual memory is an OS abstracted addressable space accessible by your code. Amr Ali Abdel-Naby@2011 Introduction to C Programming 81

Physical Memory Considerations Different sizes and access speeds Memory management is a major OS function. You have to optimize your code to make the best usage of the physical memory. OS moves data around physical memory during execution. In embedded systems, it may be very limited. Amr Ali Abdel-Naby@2011 Introduction to C Programming 82

Virtual Memory How much physical memory do you have? How much virtual memory do you have? Depends on OS Usable parts of virtual memory are stack and heap. Amr Ali Abdel-Naby@2011 Introduction to C Programming 83

Addressing Variables Every variables has an address in memory. What does not have an address? Register variables Expressions unless result is a variable. Constants, literals, and preprocessors The & operator finds the address of a variable. Address of a variable of type t has type t *. Amr Ali Abdel-Naby@2011 Introduction to C Programming 84

Dereferencing Pointers Using the * operator, I can access and modify addressed variable. A pointer that dereferences nothing is called a NULL pointer. Amr Ali Abdel-Naby@2011 Introduction to C Programming 85

Casting Pointers Explicitly from any type to any type. Implicitly to and from void *. May cause segmentation faults and many difficult errors to debug. Amr Ali Abdel-Naby@2011 Introduction to C Programming 86

Functions with Multiple Outputs Recall extended Ecluid, it calculates g = gcd(a,b) and sets the global variables x and y. Using pointers we can, extend the outputs of a function. Amr Ali Abdel-Naby@2011 Introduction to C Programming 87

Accessing Caller’s Variables Amr Ali Abdel-Naby@2011 Introduction to C Programming 88

Variable Passing Out of Scope What is wrong with this code? Amr Ali Abdel-Naby@2011 Introduction to C Programming 89

Pointer to Pointers Address stored by a pointer is also data in memory. A pointer to a pointer can address location of address in memory. Uses in C: Pointer arrays String arrays Amr Ali Abdel-Naby@2011 Introduction to C Programming 90

Pointer to Pointers Example Amr Ali Abdel-Naby@2011 Introduction to C Programming 91 vs.

Arrays and Pointers Arrays in C are implemented using a pointer to block of contiguous memory. [] can be used for accessing array elements. Array name is a pointer to its 1st element. Not modifiable/reassignable like any pointer. Amr Ali Abdel-Naby@2011 Introduction to C Programming 93

The sizeof() Operator Can be used to find the byte size of: A primitive type/variable Primitive arrays How to find array length? Amr Ali Abdel-Naby@2011 Introduction to C Programming 94

Pointer Arithmetic A pointer is not an integer but we can add/substract an integer from it. pa + i points to arr[i]; Address value increments by i x size of data type. If arr[0] has address 100, then pa + 3 has value of 112. Amr Ali Abdel-Naby@2011 Introduction to C Programming 95

Strings as Arrays Strings are null terminated character arrays. There are some utilities defined in string.h. strcpy strncpy strcmp strncmp strlen strcat strncat strchr strrchr … Amr Ali Abdel-Naby@2011 Introduction to C Programming 96

Pointer Arrays Array of pointers Each pointer can point to another array. Example usage: An array int arr[100] that we want to sort without modifying Solution: Declare a pointer array int * sorted_arr[100] containing pointers to elements of arr. Sort the pointers instead of the numbers themselves. Good approach for sorting arrays whose elements are very large. Amr Ali Abdel-Naby@2011 Introduction to C Programming 97

String Arrays An array of strings, each stored as a pointer to an array of chars. Amr Ali Abdel-Naby@2011 Introduction to C Programming 98

Multidimensional Arrays C also permits multidimensional arrays specified using []. Higher dimensions are possible. Multidimensional arrays are rectangular. Pointer arrays can be arbitrary shaped. Amr Ali Abdel-Naby@2011 Introduction to C Programming 99

Linear Search Amr Ali Abdel-Naby@2011 Introduction to C Programming 101

Binary Search Amr Ali Abdel-Naby@2011 Introduction to C Programming 102

Binary Search cont’d Requires random access to array memory Slow on sequential devices like hard disks May be wasteful Linear search may be useful in some cases. Implemented in C standard library bsearch in stdlib.h Amr Ali Abdel-Naby@2011 Introduction to C Programming 103

Simple Sort Iterate through an array until an out of order element found. Insert out of order element into correct location. Repeat until end of array reached. Amr Ali Abdel-Naby@2011 Introduction to C Programming 104

Finding Out of Order Elements Amr Ali Abdel-Naby@2011 Introduction to C Programming 105

Shifting Out of Order Elements Amr Ali Abdel-Naby@2011 Introduction to C Programming 106

Quick Sort Choose a pivot element. Move all elements less than pivot to one side. Greater ones are on other side. Sort sides individually. Implemented in C standard library qsort in stdlib.h Amr Ali Abdel-Naby@2011 Introduction to C Programming 107

Quick Sort cont’d Not stable Equal-valued elements can get switched. Can sort in-place Desirable for low-memory environments Choice of pivot influences performance. Easily parallelizable Recursive Can cause stack overflow on large array Amr Ali Abdel-Naby@2011 Introduction to C Programming 108

Exercise 4 Required: In assn-04.pdf, solve all problems except 4.3. Duration: 20 minutes Amr Ali Abdel-Naby@2011 Introduction to C Programming 109

Structure A collection of related variables grouped under a single name. Amr Ali Abdel-Naby@2011 Introduction to C Programming 111

Structure cont’d struct defines a new data type. The name of the structure is optional. The variables declared within a structure are called its members. Variables can be declared like any other built in data-type. Initialization is done by specifying values of every member. Assignment operator copies every member of the structure. Be careful with pointers. Amr Ali Abdel-Naby@2011 Introduction to C Programming 112

Accessing Structure Members The . operator is used to access structure members. Amr Ali Abdel-Naby@2011 Introduction to C Programming 113

Structure Pointers Structures are copied element wise. For large structures it is more efficient to pass pointers. Members can be accesses from structure pointers using the -> operator. Amr Ali Abdel-Naby@2011 Introduction to C Programming 114

Array of Structures Amr Ali Abdel-Naby@2011 Introduction to C Programming 115

Size of Structures The size of a structure is greater than or equal to the sum of the sizes of its members. Alignment and padding are issues. Libraries Precompiled files SIMD instructions Members can be explicitly aligned or padded using compiler extensions. Amr Ali Abdel-Naby@2011 Introduction to C Programming 116

Union May hold objects of different types/sizes in the same memory location. Union size is equal to the size of its largest element. The compiler does not test if the data is being read in the correct format. Amr Ali Abdel-Naby@2011 Introduction to C Programming 117

Bit Fields A bit-field is a set of adjacent bits within a single word. It must be unsigned int. The number after: specifies the width Amr Ali Abdel-Naby@2011 Introduction to C Programming 118

Dynamic Memory Allocation malloc() allocates an uninitialized block of memory. calloc() allocates a zero initialized array of n elements. free() frees allocated memory. Common errors: Accessing freed memory Accessing uninitialized pointer Memory leak Amr Ali Abdel-Naby@2011 Introduction to C Programming 120

Linked List A dynamic data structure that consists of a sequence of records where each element contains a link to the next and may be previous record in the sequence. They can be: Single Double Circular Amr Ali Abdel-Naby@2011 Introduction to C Programming 121

Single Linked List Every node has a payload and a link to the next node in the list. The start (head) of the list is maintained in a separate variable. End of the list is indicated by NULL (sentinel). Amr Ali Abdel-Naby@2011 Introduction to C Programming 122

Single Linked List Utilities Amr Ali Abdel-Naby@2011 Introduction to C Programming 123

Binary Tree A dynamic data structure where each node has at most two children. A binary search tree is a binary tree with ordering among its children. Usually, all elements in the left subtree are less than the root element while elements in the right subtree are greater than the root element. Amr Ali Abdel-Naby@2011 Introduction to C Programming 124

Binary Tree Utilities Can be framed as recursive Traversal (printing, searching): Pre-order: root, left subtree, right subtree In order: left subtree, root, right subtree Post order: left subtree , right subtree, root Amr Ali Abdel-Naby@2011 Introduction to C Programming 125

Exercise 5 Required: In assn-05.pdf, solve all problems. Duration: 60 minutes Amr Ali Abdel-Naby@2011 Introduction to C Programming 126

Stack A special type of list where we read and write from same end of list. LIFO list Push operation writes to list end. POP operation reads from list end. Can be build as an array or as a linked list. Amr Ali Abdel-Naby@2011 Introduction to C Programming 127

Stack as an Array Amr Ali Abdel-Naby@2011 Introduction to C Programming 128

Stack as a Linked List Amr Ali Abdel-Naby@2011 Introduction to C Programming 129

Queue A special type of list where we read and write from different ends of list. FIFO list Enqueue operation writes to list end. Dequeue operation reads from other list end. Can be build as an array or as a linked list. Amr Ali Abdel-Naby@2011 Introduction to C Programming 130

Queue as an Array Amr Ali Abdel-Naby@2011 Introduction to C Programming 131

Queue as a Linked List Amr Ali Abdel-Naby@2011 Introduction to C Programming 132

B Tree Generalized binary search tree, used for databases and file systems With variable number of children Tree is balanced. All leaves at same level A node contains a list of keys to divide range of elements in children. Initially, it contains a root node with no children. Amr Ali Abdel-Naby@2011 Introduction to C Programming 133

Inserting Elements Complicated due to maximum number of keys At high level: Traverse tree to leaf node If leaf full, split into two Move median key element into parent and split parent if already full Split remaining keys into 2 leaves Add elements to sorted list of keys Can be done in one pass by splitting full parents during traversal in step 1 Amr Ali Abdel-Naby@2011 Introduction to C Programming 134

Insertion Example Amr Ali Abdel-Naby@2011 Introduction to C Programming 135

Insertion Example cont’d Amr Ali Abdel-Naby@2011 Introduction to C Programming 136

Searching a B Tree Like searching a B Tree Start at root If node empty, element not in tree Search list of keys for element (using linear or binary search) If element in list, return element Otherwise, element between keys, and repeat search on child node for that range Amr Ali Abdel-Naby@2011 Introduction to C Programming 137

Deleting Elements Complicated due to minimum number of children restriction You need to ensure child nodes to be traversed have enough keys If adjacent child node has at least t keys, move separating key from parent to child and closest key in adjacent child to parent If no adjacent child nodes have extra keys, merge child node with adjacent child When removing a key from a node with children, need to rearrange keys again If child before or after removed key has enough keys, move closest key from child to parent If neither child has enough keys, merge both children If child not a leaf, have to repeat this process Amr Ali Abdel-Naby@2011 Introduction to C Programming 138

Deletion Example Amr Ali Abdel-Naby@2011 Introduction to C Programming 139

Deletion Example cont’d Amr Ali Abdel-Naby@2011 Introduction to C Programming 140

Priority Queue A queue where ordering data by priority, used for sorting, event simulation, and many other algorithms Elements enqueued with priority, dequeued in order of highest priority Common implementations: heap or binary search tree Amr Ali Abdel-Naby@2011 Introduction to C Programming 141

Heaps A tree with high-ordering property Child priority ≤ Parent priority Usually implemented as an array with top element at beginning Amr Ali Abdel-Naby@2011 Introduction to C Programming 142

Extracting Data Maximum priority element at top of heap Can peek by looking at top element We can remove top element, move last element to top, and swap top element down with its children until it satisfies heap-ordering property: Start at top Find largest of element and children; if element is largest, we are done Otherwise, swap element with largest child and repeat with element in new position Amr Ali Abdel-Naby@2011 Introduction to C Programming 143

Inserting Data/Increasing Priority Element is inserted at the end. Increase priority of element to real priority. Start at element If new priority less than parent’s, we are done. Otherwise, swap element with parent and repeat. Amr Ali Abdel-Naby@2011 Introduction to C Programming 144

Inserting Example Amr Ali Abdel-Naby@2011 Introduction to C Programming 145

Void Pointers C does not allow to declare and usage of void pointers. Can be used as a return type or as a function parameter C allows void pointers. The can point to any data point. They can’t be dereferenced. They must be cast before used. Amr Ali Abdel-Naby@2011 Introduction to C Programming 147

Function Pointers In C, function itself is not a variable. It is possible to declare pointer to functions. Declaration examples: Function pointers can be assigned, pass to and from functions, placed in arrays etc. Amr Ali Abdel-Naby@2011 Introduction to C Programming 148

Callbacks A piece of executable code passed to functions. Callbacks are implemented by passing function pointers. Example: qsort() can sort an array of any data type. qsort() calls a function whenever a comparison needs to be done. Callback The callback returns <0, 0, or >0 depending on iinputs. Amr Ali Abdel-Naby@2011 Introduction to C Programming 149

qsort Callback Amr Ali Abdel-Naby@2011 Introduction to C Programming 150

Linked List Callback We can make a callback that iterates a function through the list. Amr Ali Abdel-Naby@2011 Introduction to C Programming 151

Printing and Counting Nodes Amr Ali Abdel-Naby@2011 Introduction to C Programming 152

Array of Function Pointers Amr Ali Abdel-Naby@2011 Introduction to C Programming 153

Array of Function Pointers cont'd Amr Ali Abdel-Naby@2011 Introduction to C Programming 154

Hash Table Combines linked lists and arrays to provide an efficient structure for storing dynamic data. They are commonly implemented as an array of linked lists. Amr Ali Abdel-Naby@2011 Introduction to C Programming 156

Hash Table cont'd Each data item is associated with a key that determines its location. Hash functions are used to generate an evenly distributed hash value. A hash collision is said to occur when two items have the same hash value. Items with the same hash keys are chained Amr Ali Abdel-Naby@2011 Introduction to C Programming 157

Hash Functions A hash function maps its input into a finite range: hash value, hash code. The hash value should ideally have uniform distribution. Other uses of hash functions: cryptography, caches (computers/internet)… Hash function types: Division type Multiplication type … Amr Ali Abdel-Naby@2011 Introduction to C Programming 158

Hash Table Example Amr Ali Abdel-Naby@2011 Introduction to C Programming 159

Hash Table Example Amr Ali Abdel-Naby@2011 Introduction to C Programming 160

Symbols and Libraries External libraries provide a wealth of functionality . C standard library Programs access libraries’ functions and variables via identifiers known as symbols. Header file declarations/prototypes mapped to symbols at compile time. Symbols linked to definitions in external libraries during linking. Our own program produces symbols too. Amr Ali Abdel-Naby@2011 Introduction to C Programming 162

Functions and Variables as Symbols What variables and functions are declared globally? Amr Ali Abdel-Naby@2011 Introduction to C Programming 163

C Compilation Process Amr Ali Abdel-Naby@2011 Introduction to C Programming 164

Static and Dynamic Linking Functions, global variables must be allocated memory before used. Can allocate at compile time (static) or at run time (shared) Static linking links symbols in .o files and .lib files. Dynamic linking uses symbols in .dll files. Amr Ali Abdel-Naby@2011 Introduction to C Programming 165

Static vs. Dynamic Linking Static During compile time Linked symbols are added to executable. Larger executable No libraries’ dependencies on run time Library upgrade needs recompilation. Dynamic During run time Linked symbols are loaded from shared library. Smaller executable Depends on shared libraries location on run time. No recompilation needed Amr Ali Abdel-Naby@2011 Introduction to C Programming 166

Symbol Resolution Issues Symbols can be defined in multiple places. Suppose we define our own puts() function . But, puts() is defined in C standard library. Which puts compiler uses? Dynamic linking uses our puts as C standard library is known at run time only. Statically linking against C standard library causes an error. Amr Ali Abdel-Naby@2011 Introduction to C Programming 167

Standard Library <stdio.h> <ctype.h> <stdlib.h> <string.h> <assert.h> <stdarg.h> <time.h> … Amr Ali Abdel-Naby@2011 Introduction to C Programming 169

<stdio.h> fopen freopen fflush rename remove tmpfile tmpname fread fwrite fseek ftell rewind clearerr feof ferror Amr Ali Abdel-Naby@2011 Introduction to C Programming 170

<ctype.h> isalnum isctrl isdigit islower isprint ispunct isspace isupper Amr Ali Abdel-Naby@2011 Introduction to C Programming 171

<string.h> memcpy memmove memcmp memset Amr Ali Abdel-Naby@2011 Introduction to C Programming 172

<stdlib.h> atof atoi atol rand srand abort exit atexit system bsearch qsort Amr Ali Abdel-Naby@2011 Introduction to C Programming 173

<assert.h> assert Amr Ali Abdel-Naby@2011 Introduction to C Programming 174

<time.h> clock time difftime mktime asctime localtime ctime strftime Amr Ali Abdel-Naby@2011 Introduction to C Programming 175

Project II: BMP to JPEG Tool Amr Ali Abdel-Naby@2011 Introduction to C Programming 176 Required: Write a utility that converts a bmp image to a jpeg image. Deadline: A week from now References: http://en.wikipedia.org/wiki/BMP_file_format http://en.wikipedia.org/wiki/JPEG http://www.digicamsoft.com/itu/itu-t81-36.html http://www.cs.cf.ac.uk/Dave/Multimedia/node234.html http://www.w3.org/Graphics/JPEG/jfif3.pdf Bmp to jpeg utility

BMP File Format File header Image header Color table GAP1 Pixel array GAP2 Color profile Amr Ali Abdel-Naby@2011 Introduction to C Programming 177

BMP File Header Signature: 2 bytes “BM” File size: 4 bytes File size in bytes Reserved 1 and 2: Each 2 bytes Used by the image creator application File offset to pixel array: 4 bytes Offset from file start to pixel array Amr Ali Abdel-Naby@2011 Introduction to C Programming 178

BMP Image Header Each field is either 4 bytes or 2 bytes. Color space endpoints is 36 bytes. Planes must be 1. Bits per pixel can be 1, 4, 8, 16, 24, and 32. We will only focus on uncompressed bmp. Important color count is usually ignored. Masks can be used to extract data from pixels. Amr Ali Abdel-Naby@2011 Introduction to C Programming 179

BMP Color Table Mandatory when bits per pixel are less than 8. It defines colors used in the bitmap. Can be used to index bitmap images. A table entry is either 4 bytes or 3 bytes depending on the header version. Amr Ali Abdel-Naby@2011 Introduction to C Programming 180

BMP Pixels Amr Ali Abdel-Naby@2011 Introduction to C Programming 181

JPEG Compression Color space transformation Downsampling Discrete cosine transform Quantization Zigzag scanning DPCM on DC components RLE on AC components Entropy Coding Amr Ali Abdel-Naby@2011 Introduction to C Programming 182

Color Space Transformation and Downsampling Transforming RGB to YCbCr YCbCr allows reduction in Cb and Cr components. Downsampling Known Downsampling are: 4:4:4 4:2:2 4:2:0 Amr Ali Abdel-Naby@2011 Introduction to C Programming 183

Discrete Cosine Transform For 8×8 block, its values are shifted from a positive range to one centered around zero before computing the DCT. DCT is performed after shifting as follows: Amr Ali Abdel-Naby@2011 Introduction to C Programming 184

Quantization Dividing DCT output with quantization matrix. The output will is rounding of quantization. Amr Ali Abdel-Naby@2011 Introduction to C Programming 185

Zigzag Scanning Maps 8x8 matrix into a vector Amr Ali Abdel-Naby@2011 Introduction to C Programming 186

DPCM and RLE DPCM: Store the difference between the current DC value and the previous one RLE: Encode the AC values as pairs of (skip, value). Skip is the number of preceding zeroes. Value is the next non-zero value. (0,0) is used as end of block. Amr Ali Abdel-Naby@2011 Introduction to C Programming 187

Entropy Coding Categorize DC values into SSS Send off SSS as Huffman symbol, followed by actual 3 bits. For AC components (skip, value), encode the composite symbol (skip, SSS) using the Huffman coding. Huffman Tables can be custom (sent in header) or default. Amr Ali Abdel-Naby@2011 Introduction to C Programming 188

JPEG File Format Let’s check http://www.w3.org/Graphics/JPEG/jfif3.pdf Amr Ali Abdel-Naby@2011 Introduction to C Programming 189

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