Introduction to C

C is a general-purpose, compiled programming language created by Dennis Ritchie at Bell Labs in the early 1970s. It grew alongside Unix: a small language could express operating-system code efficiently while remaining portable across machines. Modern C is standardized by ISO; important editions include C89/C90, C99, C11, C17, and C23. Compilers may support different editions, so production projects should state the standard they require.

Why C still matters

C exposes a compact abstraction over machine memory. It offers structured control flow, functions, arrays, structures, pointers, and a small standard library without automatic garbage collection or a large runtime. That makes it common in operating systems, embedded firmware, device drivers, databases, language runtimes, networking libraries, and performance-critical components.

Its strengths—predictable layout, direct memory access, portability, and mature tooling—also create responsibility. The programmer must respect object lifetimes, array bounds, types, and resource ownership. C is not “unsafe by default” so much as explicit by default.

From source to executable

A typical build passes through four conceptual stages:

1. The preprocessor expands directives such as #include and macros.
2. The compiler parses and translates C into assembly or object code.
3. The assembler creates machine-code object files.
4. The linker combines objects and libraries, resolving external names.

With GCC or Clang, one command usually drives all stages:

cc -std=c17 -Wall -Wextra -Wpedantic hello.c -o hello
./hello

On Windows, use a supported toolchain such as Visual Studio’s MSVC, LLVM/Clang, or GCC through MSYS2. An editor is not a compiler; configure both the editor and toolchain, then verify cc --version or the equivalent command.

Your first program

#include <stdio.h>

int main(void) {
    puts("Hello, C!");
    return 0;
}

stdio.h declares the standard input/output functions. main is the hosted program entry point. puts writes a line, and returning 0 reports success to the environment.

Build for feedback

Warnings are part of the development workflow, not cosmetic noise. A practical debug build is:

cc -std=c17 -Wall -Wextra -Wpedantic -Wconversion -g main.c -o app

During testing, Clang and GCC sanitizers can expose invalid memory use and undefined behavior:

cc -std=c17 -g -fsanitize=address,undefined main.c -o app

Compile often, read the first diagnostic first, and keep programs small while learning. Every later chapter builds on this toolchain.