A compiler transforms a program into another representation. An interpreter executes a representation of a program. Real implementations often combine those ideas, so calling a language simply “compiled” or “interpreted” can hide more than it explains. C is commonly compiled ahead of execution, but the full path still depends on the target.
Separate a language from its implementation
A programming language defines constructs and their meaning. An implementation decides how to translate or execute valid programs on a particular platform. The same language can have more than one implementation strategy, and one implementation can change its strategy between development and production.
For ordinary C work, a compiler and linker produce target code before you launch the program. That is a useful practical model, not a universal rule that every possible C implementation must emit a native executable file. Circuit is a concrete alternative: Clang produces WebAssembly that a browser engine executes.
Ahead-of-time compilation
An ahead-of-time compiler performs translation before the relevant execution. It can report syntax and type problems without running the program and can optimize the generated representation. Native toolchains commonly produce an executable designed for a particular operating system and architecture.
The resulting artifact may depend on shared libraries or runtime support. “Compiled” does not mean completely self-contained. A binary built for one target will not necessarily run on another, and source portability still depends on the libraries and environmental assumptions used by the program.
Interpretation
An interpreter carries out program operations through another executing program. It may parse source first, build a syntax tree, or consume bytecode. The popular description “reads one source line at a time” is too narrow: interpreters frequently do substantial preparation and do not treat physical lines as execution units.
Interpretation can make interactive experimentation convenient, but convenience does not prove that every operation is slower or that no translation occurs. Startup work, caching, native library calls, and the workload itself all affect observed performance. Compare actual implementations rather than relying on a slogan.
Bytecode and just-in-time compilation
Some systems translate source to bytecode, then interpret or compile that bytecode as needed. A just-in-time compiler generates target instructions during execution, potentially using information about frequently executed paths. These approaches combine translation with runtime decisions.
A browser’s WebAssembly engine may use more than one compilation tier. Circuit first compiles C to a WebAssembly module; the engine then prepares that module for execution. The fact that the program runs in a browser does not mean Circuit is reading C statements and pretending to execute them in JavaScript.
Error timing differs, but testing remains necessary
Compilation can catch many problems before a run, including malformed syntax and incompatible declarations. It cannot generally decide whether every possible input will produce the intended result. A division, index, or loop condition may only become problematic for a particular runtime value.
Interpreted systems can also reject source before executing its first meaningful operation. Conversely, compiled programs can fail after hours of execution. Classify errors by the actual stage and operation, not by assuming that all mistakes in one category happen early or late.
Performance has several costs
For a short interactive exercise, downloading a toolchain and compiling a module may take longer than running the algorithm. For a long-running numerical task, generated code quality and memory access patterns may dominate. Measure startup, translation, and execution separately when those distinctions matter.
Optimization levels can also change translation time and runtime behavior for valid programs. An optimized build is not automatically easier to debug, and undefined behavior can become more visible under optimization. Circuit currently uses -O0 for its C compilation, so its timings are not a benchmark for every possible Clang configuration.
Choose tools around the job
For learning C expressions, functions, and standard input, a browser compiler offers a short setup path. For large projects, native dependencies, deep debugging, or operating-system integration, a local toolchain offers a different set of capabilities. Neither choice makes the underlying learning more or less legitimate.
Try the same small function with known inputs in both environments if you have them. Compare results before comparing speed, and check target differences such as type sizes and available APIs. The useful question is which implementation supports your task and constraints, not which label sounds more powerful.