C Programming PDF Download – Wikibooks (BSCS/BSIT)

BSCS and BSIT students can read and download the complete “C Programming” textbook written and maintained by Wikibooks contributors, free from its official source. C is a required first- or second-semester course at almost every Pakistani university offering these degrees, and this book covers the full syllabus — from the very first program through pointers, dynamic memory and the standard library.

The book is organised into five parts that build on each other: Introduction, Beginning C, Intermediate C, Advanced C, and C and Beyond, plus reference tables and appendices for quick lookup. Because it is a wiki rather than a fixed edition, it is continuously reviewed and corrected by its contributors, and Wikibooks itself has featured it as one of its best-formatted, most complete books. Students preparing for board exams, entry tests or a first industry interview will find the pointer, memory and standard-library chapters especially exam-relevant.

Book Overview

Chapter List

Introduction: Why C, Its History, and Getting Set Up

Difficulty: Easy · Key topics: why learn C, Bell Labs and UNIX history, ANSI standardization, compilers, GCC

The opening part answers why a language from 1972 is still worth learning: C is the language Unix was rewritten in, it is the implementation language behind Perl, PHP, Python and Ruby, and knowing it makes the whole family of languages built on its traditions easier to read. The History page traces the real lineage — Fortran to Algol to BCPL to Ken Thompson’s B, refined at Bell Labs into C, then standardized by ANSI as X3.159-1989 after Unix’s portability made both Unix and C popular. The last two pages are practical: the book assumes no prior programming experience but does assume comfort with a command-line terminal, and it settles on GCC as the compiler used in every later example, with Dev-C++, Xcode and Visual Studio Community listed as free ways to get a compiler running.

Key Points:

• C descends from BCPL through Ken Thompson’s B language, developed for early UNIX at Bell Labs.
• The ANSI C standard (X3.159-1989) is the baseline every later “ANSI C” or “C89” compiler targets.
• Python, Perl, PHP and Ruby are themselves implemented in C.
• The book assumes zero prior programming experience, only basic command-line familiarity.
• GCC (the GNU Compiler Collection) is the compiler used in every code example in the book.
• Free compiler/IDE options listed: Dev-C++ and Visual Studio Community (Windows), Xcode (macOS).

Practice Tip: Install GCC and compile your first program from the command line rather than through an IDE — gcc hello.c -o hello then ./hello — exactly as the book itself recommends for beginners.

Common Mistake: Treating an IDE like Dev-C++ as the compiler. The book is explicit that Dev-C++ is only an editor and front end — it still needs MinGW or Cygwin’s build of GCC underneath to actually compile anything.

Important Questions:

• Why is learning C still useful when higher-level languages exist? Because C is the foundation Unix and Linux are built on and the implementation language behind Python, Perl, PHP and Ruby, so understanding C makes the whole family of languages built on its traditions easier to learn.
• What compiler does this book use for its examples, and how do you get it? GCC — installed directly on Linux, via the Xcode command-line tools on macOS, or via MinGW/Cygwin (bundled with Dev-C++) on Windows.

Beginning C: Syntax, Variables, Control Flow, and Functions

Difficulty: Easy · Key topics: statements and semicolons, comments, stack and heap, data types, operators, arrays and strings, conditionals, loops, functions

This part is the semester-one syllabus, read start to finish: every statement in C ends with a semicolon inside a “free-format” language where whitespace between tokens is ignored, and comments come as // single-line or /* */ multi-line. Variables are introduced as named memory locations that live in CPU registers or in the stack (short-lived) and heap (longer-lived) regions of RAM. Arrays are declared as type name[size], indexed from 0, and get no automatic bounds checking; strings are simply arrays of char. Program Flow Control treats logic as arithmetic — 0 means false, anything else means true — before covering if-else, switch-case and loops, and the part closes with procedures, functions and the standard library headers that give access to them.

Key Points:

• Every C statement ends with a semicolon; C is “free-format”, so whitespace between tokens does not matter.
• Variables live in CPU registers, or in the stack (short-lived data) or heap (longer-lived data) portions of RAM.
• Arrays are declared as type name[size] and are indexed from 0, with no automatic bounds checking.
• A string is just an array of char ending in the null character \0, not its own data type.
• C treats logic as arithmetic: the value 0 means false, and every other value means true.
• A code block is delimited with { and } and needs no semicolon after the closing brace.

Practice Tip: Deliberately declare int numbers[5]; and then write to numbers[10] — GCC will compile it without complaint and silently corrupt nearby memory, which is the fastest way to feel why “no bounds checking” matters.

Common Mistake: Leaving off the trailing semicolon. The book calls this out directly as a mistake “many people make, beginners and experts alike.”

Important Questions:

• Can a C variable name start with a digit? No — an identifier must start with a letter or underscore, and may only be followed by letters, digits or underscores.
• Why doesn’t C stop you from reading or writing past the end of an array? Because a C array does not store its own length — it is just a block of contiguous memory, so an out-of-range index reads or writes whatever memory happens to sit at that address instead of raising an error.

Intermediate C: Structs, Pointers, Memory, and Error Handling

Difficulty: Medium · Key topics: structs and typedef, pointers and dereferencing, malloc/free, errno, string escapes

Intermediate C is where most Pakistani university C/Data Structures exams actually draw their questions from. Advanced Data Types introduces struct to group related variables (“members”) under one name, with typedef used to give the type a shorter alias. Pointers and Relationship to Arrays covers the four things every pointer question tests: declaring with *, assigning an address with &, dereferencing with *, and how pointers relate to arrays. Memory Management adds malloc(), calloc(), realloc() and free() for memory whose size isn’t known until the program runs. Error Handling explains that C has no built-in exceptions — functions signal failure through return values like -1 or NULL, checked by convention and explained further with errno and strerror() — and String Manipulation covers the null terminator and the full backslash-escape table.

Key Points:

• A struct groups related variables (“members”) of possibly different types under one name, accessed with the . operator.
• typedef creates a shorter alias for a struct type so you don’t have to write struct name everywhere.
• Declaring a pointer uses * (int *p;); taking an address uses &; reading the pointed-to value uses *p (dereferencing).
• malloc(), calloc() and realloc() allocate heap memory at runtime; every successful allocation must eventually be matched with free().
• C has no built-in exception handling — functions signal errors through return values such as -1 or NULL, with errno and strerror() giving the reason.
• A C string is a char array ending in the null character \0, so "abc" actually occupies 4 bytes, not 3.

Practice Tip: After every call to malloc(), check the returned pointer against NULL before using it — the book’s own error-handling example does exactly this before touching a large block of requested memory.

Common Mistake: Forgetting to free() heap memory once it is no longer needed — the book notes this can eventually leave the operating system unable to grant the process any more memory.

Important Questions:

• What operator gets the memory address of a variable, and what is it called? The address-of operator &; applying it to a variable (e.g. &variable) gives the address to store in a pointer.
• Why must a string copied with malloc() be given strlen(s) + 1 bytes and not strlen(s)? Because a C string needs one extra byte for the terminating null character \0 that marks its end; leaving it out corrupts the byte immediately after the buffer.

Advanced C: Preprocessor, Networking, and Systems Techniques

Difficulty: Hard · Key topics: preprocessor directives, #include, dynamic multidimensional arrays, UNIX sockets, setjmp/longjmp coroutines

This part collects the techniques that come up once a program grows past a single file. Common Practices covers dynamic multidimensional arrays — allocating a rectangular 2D array as one malloc() block versus building an array of pointers (an Iliffe vector) for ragged rows. Preprocessor Directives and Macros explains that every line starting with #, including #include, is handled by a text-substitution pass that runs before the compiler ever sees your code. Sockets and Networking (UNIX) walks through a real minimal client: socket() creates a file descriptor, a sockaddr_in struct holds the destination’s address family, port (htons()) and IP, connect() reaches it, and recv() reads the reply. Coroutines closes the part with setjmp()/longjmp(), which save and restore the CPU’s registers and program counter to give C a primitive form of cooperative multitasking.

Key Points:

• The preprocessor runs before the compiler and handles every directive — any line starting with # — as a lexical, text-level substitution pass.
• #include <header.h> pulls in a standard library header so its functions (e.g. printf, malloc) become usable, and is itself a preprocessor directive.
• A rectangular dynamic 2D array can be allocated as one block with malloc(rows * sizeof(int[cols])), instead of one allocation per row.
• UNIX socket programming follows a fixed pattern: socket() creates the descriptor, connect() reaches the remote host, and recv()/send() move data.
• sockaddr_in is the struct that stores a connection’s address family, port (set via htons()) and IP address (via htonl() or INADDR_LOOPBACK).
• setjmp()/longjmp() save and restore CPU registers and the program counter, giving C a primitive form of cooperative multitasking.

Practice Tip: Type the book’s minimal socket client out by hand and run it against something listening on PORTNUM locally — watching recv() actually block until data arrives is what makes network code click.

Common Mistake: Assuming recv() null-terminates what it reads. It does not — the book’s own example manually sets buffer[len] = '\0'; after every call, and skipping this turns the next printf into undefined behaviour.

Important Questions:

• What symbol marks a preprocessor directive in C? The hash symbol # at the start of the line, as in #include, #define or #ifdef.
• What does the sockaddr_in struct hold in the book’s socket example? The destination’s address family, port number and IP address — everything connect() needs to reach a remote or local server.

C and Beyond: Language Limits, Mixing Languages, and Object-Oriented C

Difficulty: Medium · Key topics: pointer/array duality, arrays with no stored length, calling C from Python/Perl/Java, simulating OOP with GObject

The closing part is honest about where C stops and other tools take over. Particularities of C explains that early C had no true arrays at all — modern C arrays are contiguous memory accessed through pointer arithmetic, and because they don’t store their own length, any function that receives one needs the size passed separately. Combining Languages then shows three real bridges out of C: Python’s ctypes module calls a C function directly without writing an extension, Perl’s XS interface (built with the h2xs tool) does the same for Perl, and Java reaches C libraries through JNI. GObject closes the book by showing how plain C, which has no classes or inheritance of its own, gets them back through a third-party library — GObject (part of GLib) — using structs, function pointers and a hand-built virtual table, declared with macros like G_DECLARE_FINAL_TYPE.

Key Points:

• Early C had no true arrays; modern C arrays are contiguous memory accessed by pointer arithmetic, and a declared array (unlike a pointer) cannot be reassigned.
• Because arrays don’t store their own length, a function that receives one must also be given its size separately.
• Python’s ctypes module calls C functions directly from Python without writing a C extension.
• Perl’s XS interface, built with the h2xs tool, is the standard way to call C code from Perl.
• Java reaches C libraries through JNI — the Java Native Interface.
• C has no classes or inheritance of its own; the GObject library adds them using structs, function pointers and a hand-built virtual table.

Memory Tip: Remember the three cross-language bridges by their own host language’s name for the idea: ctypes for Python, XS for Perl, JNI for Java — each is simply “how that language’s interpreter calls a C function.”

Common Mistake: Assuming sizeof(array) still works after the array is passed into a function. Once passed as an argument it decays to a plain pointer, and sizeof on a pointer just returns the pointer’s own size, not the array’s.

Important Questions:

• Why can’t a C function tell how long an array is just by receiving it? Because arrays don’t store their length in memory — the function only receives a pointer to the first element, so the caller must pass the length separately.
• How can a C library be used from a language like Python without rewriting it? Through a language bridge — Python’s ctypes module, for example, lets Python code call functions in a compiled C library directly, without writing a dedicated C extension module.

Download C Programming PDF (Free)

Click below to download the official Wikibooks e-reader PDF edition (719 pages, generated directly from the wiki by the Wikimedia Foundation’s own MediaWiki2LaTeX tool). Because Wikibooks is a living, continuously edited project, this PDF is a snapshot from 2012 — the C fundamentals it teaches have not changed, but every page has been edited many times since, so if you want the exact current wording, read the always-current online edition instead. Both are official and both are free.

How to Study This Book

Start with the Introduction. It’s short, but it settles the one practical decision every reader needs made before writing a line of code — which compiler to install — and this book’s own examples all assume GCC, so match that if you can.

Beginning C is the actual semester-one syllabus, and it should be read in the order the book gives it: Preliminaries and Basics of Compilation, then Variables, Simple Input and Output, Operators and type casting, Arrays and Strings, Program Flow Control, and Procedures and Functions. Do the exercises attached to each page as you finish it, not at the end — the book’s own “Beginning exercises” page groups practice questions by exactly these topics.

Intermediate C carries the most exam weight in a typical Pakistani university C or Data Structures course. Read Advanced Data Types (structs) before Pointers and Relationship to Arrays, because the pointer examples use structs freely once they’re introduced. Memory Management and Error Handling go together — every malloc() example in this book is immediately followed by a NULL check, and that habit is worth copying from day one.

Advanced C is elective-depth material. Most BSCS/BSIT courses only need Preprocessor Directives and Macros; treat Sockets and Networking (UNIX) and Coroutines as optional unless your own course outline specifically covers systems or network programming.

C and Beyond and the book’s Reference Tables, Platform Reference and Appendices are lookup material, not a cover-to-cover syllabus. Keep the Language Reference and the Table of Operators open in a second tab while you work through exercises instead of trying to memorize them up front, and check the Exercise Solutions appendix only after attempting a problem yourself.

Because this is a wiki with no fixed chapter numbers, map each part above onto whatever your own course outline calls “Week 1”, “Week 2” and so on — the order given here matches how the book itself is meant to be read, front to back.

Used In These Programs

This book is used for the C Programming course in: BS Computer Science · BS Information Technology. Browse all Programming books or all Computer Science books.

Who Should Read This

This book is written for students taking their first Programming Fundamentals or C Programming course, typically in the first or second semester of BSCS or BSIT. The Beginning C part assumes absolutely no prior programming experience, so it works equally well as a first language and as a refresher for students who have seen another language already. It is not a book for someone who wants a gentle, hand-held introduction with heavy hand-holding on every line — the tone stays fairly technical throughout, so readers who prefer a slower, more narrative style may want a supplementary text alongside it. Once you finish Intermediate C and Advanced C here, the natural next step is to see this same language power a real operating system — Operating Systems: Three Easy Pieces uses C throughout and builds directly on the pointers, memory management and systems thinking this book teaches.

Applicable Universities

This book is useful for students at Pakistani universities offering BSCS and BSIT including Punjab University, Virtual University, COMSATS, FAST, UET, NUST, and other HEC-recognized institutions.

FAQs

Related Books

• Operating Systems: Three Easy Pieces – Arpaci-Dusseau
• Data Structures in C++ – Aikman Series
• Computer Networking: Principles, Protocols and Practice – Bonaventure
• Object Oriented Programming Using C++ – IT Series

C Programming (Wikibooks) is a solid, exam-focused way to cover a full university C course for free — it moves from your first program to pointers, dynamic memory and systems-level techniques without skipping the syntax details Pakistani university exams actually test. Because it is continuously maintained by its contributors, it stays accurate without needing a new edition. Browse more Computer Science books for the rest of your semester.

C Programming, by Wikibooks contributors. Published by Wikibooks, a Wikimedia Foundation project, continuously updated. Free under the Creative Commons Attribution-ShareAlike 4.0 International licence. Official source: https://en.wikibooks.org/wiki/C_programming