Lecture 3 Introduction to C Programming

Why Learn C?

• C is a low-level language suited for data and hardware manipulation (device drivers, O/S modules, embedded systems).
• It's small, simple, consistent, and cohesive, designed by Denis Ritchie at Bell Labs, initially described in a 261-page book.
• C features a huge code-base and a standard tool-chain, making it the language of choice for system programming.

Why Learn C? (Really)

• C requires understanding of the system and machine operations and doesn't conceal anything.
• Implementation of data structures is required, so awareness of all trade-offs is gained.
• C forces the user to look "under the hood".

Where to Start Learning C?

• C has similarities with languages like Java, as many languages are derived from C.
• The syntax is nearly identical in loops, if statements, local variables, expressions, etc and execution starts in main().
• Operations, such as output are very similar to Java.

Alternative Start To Learning C

• There is existing knowledge of C code due to familiarity with Java.
• Study should focus on organization of C programs (code/header files), the build process, and C commandments.

C File Composition

• C programs consist of code files (.c) and header files (.h).
• Header files contain definitions and information about run-time artifacts (function and variable declarations).
• Code files contain both compile-time and run-time artifacts, being those used when the program is compiled or running, global or static functions and variables.
• Header files are included by other files.

Header Files and #include

• A header file is "included" via the #include statement, inserting the header file content at compile time.
• #include includes standard library header files, while #include "file" includes program-specific header files.
• Header files may include other header files as well.

Why Header Files?

• Necessary because the C build process compiles each C file independently.
• They avoid duplicate type definitions across files and provide a manifest of runtime artifacts.

Avoiding Duplicate Type Declarations

• Type declarations are used at compile time.
• Defining a type in multiple code files leads to errors.
• Use header files to define a type used by multiple code files.

Manifest of a Code File

• The C compiler can only process one file at a time, and cannot do error checking if a function or variable is used from another file.
• Header files act as manifests containing type definitions, function declarations, and variable declarations.
• The header file containing the "manifest" is included by code files that use those types, functions and variables.
• It's a best practice for header file and code file names to match, and for code files to include their corresponding header files (e.g., stack.c includes stack.h).

The C Build Process

• The build process includes preprocessing, compiling, assembling, and linking.

Larger Programs

• Compiling commands will look like: gcc –Wall –o reverse main.c stack.c
• The code base of a larger project consist of: main.c, stack.c, stack.h and node.h

Individually Compiled C Files

• Key concept is that each C file is compiled individually without reading other C files except for included header files during preprocessing.

Linker Role

• The linker builds the executable from object files and standard libraries (stdio, stdlib).
• The linker expects a main function as the starting point.

Key Differences From Java

• Java performs linking at runtime.
• Java (.java) files are compiled into class (.class) files individually.
• Type information is stored and used, as a runtime artifact, in the class files.
• Class files run to link classes at runtime.

The C Commandments

• Never put function or variable definitions in header files to avoid multiple definitions.
• Every code file (besides the one with main()) should have a corresponding header file.
• Declare all functions and variables used outside of a code file in the corresponding header file.

Learning Through Coding in C

• Knowledge of Java can accelerate learning C.
• Writing programs to identify and address the differences promotes learning.
• Initial topics: Basic I/O, arrays, strings, references (pointers).

Number Reversal Program

• Goal: Create a program (revnum) that reads a specified number of integers and outputs them in reverse order, using stdin/stdout.
• Input:
  • An integer N (followed by N integers on separate whitespace).
• Output:
  • N integers in reverse order, one per line.
• Learning:
  • Setting up main() function
  • Using scanf and printf
  • Defining and using arrays

String Reversal Program

• Goal: Create a program (revstr) that reads a specified number of words and outputs them in reverse order.
• Input:
  • An integer N, followed by N strings separated by white-space (strings are at most 49 characters).
• Output:
  • The N strings in reverse order, one per line (stdout).
• Learning:
  • String representation in C
  • Reading, storing, and writing strings
  • References in C [maybe]

Explore the fundamentals of C programming, a low-level language ideal for system programming and hardware manipulation. Understand its significance, system interaction, syntax similarities with languages like Java. Start with a foundational understanding of C and its applications.