GCC, part of the GNU Project since the late 1980s, and Clang, built on the LLVM compiler infrastructure and known for clearer error messages, are the two dominant free C compilers — both are genuinely production-grade, used to build everything from the Linux kernel to major commercial software. macOS ships Clang (via Xcode's command-line tools); Linux distributions typically ship GCC by default, though both are installable everywhere. There is no single official reference implementation the way many newer languages have.
Compiling and running by hand
-o names the output executable explicitly; without it, both compilers default to a.out (a historical name dating back to early UNIX assemblers).
$ gcc hello.c -o hello // compile with GCC
$ ./hello
Hello, World!
$ clang hello.c -o hello // or compile with Clang instead — same source, either worksEnabling warnings: -Wall -Wextra
C's default warning level is famously permissive — code with genuine bugs (an uninitialized variable, a mismatched printf format specifier) often compiles silently without these flags. Enabling them is close to universal practice in real C projects.
$ gcc -Wall -Wextra -o hello hello.c
// -Wall: enables most commonly useful warnings
// -Wextra: enables additional warnings -Wall doesn't coverChoosing a language standard explicitly
Without an explicit standard flag, the compiler's default can vary by version and vendor — specifying one directly makes a build's behavior predictable and portable across different machines and compiler versions.
$ gcc -std=c17 -Wall -Wextra -o hello hello.c // target the C17 standard explicitly