Lecture 3 Intro to C Programming

• C is a low-level language ideal for manipulating data and hardware devices, like device drivers, O/S Modules, and embedded systems.
• C is small, simple, consistent, and cohesive.
• Denis Ritchie at Bell Labs designed C.
• C was initially described in a 261-page book.
• C has a large code base and a standard tool-chain.
• C is the preferred language for system programming.
• Learning C requires an understanding of the system and machine.
• C does not abstract details.
• C requires developers to implement their own data structures, increasing awareness of trade-offs.
• C forces developers to look "under the hood."
• Many languages, including Java, derive from C.
• Starting with the traditional "Hello World" program is common.
• C and Java share similar syntax for loops, if statements, local variables, and expressions.
• Execution in both languages begins in main().
• Many operations, like output, are very similar between C and Java.

Underlying Organization

• C programs are organized into code files and header files.
• The build process in C differs significantly from Java.
• C programs are composed of two kinds of files: Code files (.c) and Header files (.h).

Header Files

• Header files contain compile-time artifacts like type definitions, information about run-time artifacts, function declarations, and variable declarations.

Code Files

• Code files contain compile-time and run-time artifacts.
• These are used when the program is being compiled or running, including global or static function/variable definitions.
• Header files are included by other files.
• A header file is included in code (or another header) using the #include statement.
• The #include statement incorporates the contents of the header file during compilation.
• During compilation, the contents of the header file replace the #include statement.
• #include <file> includes "standard library" header files.
• #include "file" includes the program's own header files.
• Header files often include other header files.

Importance of Header Files

• Header files prevent duplicate type definitions across files and provide a manifest of runtime artifacts defined in a code file.
• Header files are essential because each C file is compiled independently.
• A type declaration is only used at compile time.
• Without header files, two code files needing the same type definition would both need to define it, leading to duplicate code and errors.
• Instead, a type used by multiple code files should be defined once in a header which is included by all files that use the type.
• The C compiler processes one file at a time.

Manifest files

• If a function in one file uses a function or variable from another, the C compiler cannot perform error checking.
• Header files serve as manifests, containing type definitions, function declarations, and variable declarations.
• The header file with the "manifest" should be included by any code file using those types, functions, and variables.
• Header files should have the same name as the corresponding code file.
• Code files should include the corresponding header file, ensuring that the manifest matches the code.

C build process

• The preprocessor (cpp), compiler (cc1), assembler (as), and linker (ld) are all components of the C build process
• Each C file is compiled individually without reading other C files.
• Object files are created, but preprocessed source (.i) and assembly (.s) files are omitted.

Linker

• The linker creates the executable from object files and libraries (e.g., stdio, stdlib).
• The linker requires a main function to start the program.

Java

• Java does linking at runtime, compiling .java files into .class files, which are not combined.
• Type information is a runtime artifact stored in Java's class files.
• The Java Virtual Machine (JVM) links classes together at runtime and runs the class files.
• During compilation, the Java compiler reads other Java or class files if the current file depends on their code.

C commandments

• Never put function or variable definitions in header files to avoid multiple definitions.
• Every code file, except for the one containing main(), needs a corresponding header file.
• All functions and variables used outside a code file should be declared (not defined) in the corresponding header file.
• Learning C involves understanding its differences from Java through writing programs and discussing these differences.
• Start with basic I/O, arrays, strings, and references (pointers).

Number Reverse

• Write a program called revnum that reads in a specified number of integers and outputs them in reverse order.
• Input is from the console (stdin).
• The first line has an integer N, the number of integers to follow
• The second line is N integers separated by whitespace.
• Output is to the console (stdout) and contains the N numbers in reverse order, one per line.
• Learning outcomes include setting up the main() function, using scanf and printf for basic input/output, and defining and using arrays.

String Reverse

• Write a program called revstr that reads in a specified number of words and outputs them in reverse order.
• The first line has an integer N, the number of words to follow
• Strings are separated by white-space, and the strings are at most 49 characters
• Learning outcomes include string representation in C, reading, storing, and writing strings, and references in C.

Explore C programming's fundamentals: its role in system programming, low-level data manipulation, and hardware control. Learn about C's history, its influence on other languages like Java, and the importance of understanding system architecture for effective C development.