Languages: The characteristics of a compiler and an interpreter

The idea

A compiler translates a whole high-level program into machine code before any of it runs, producing an executable file that can be distributed and run later without the translator. An interpreter translates and executes the source one statement at a time, so it stops at the first error it meets and reports it immediately. Compilers therefore give fast execution but slow development, because each change needs a full recompile; interpreters give slower execution but allow quick testing and easier debugging. For example, a Python interpreter runs a script line by line, while a C compiler builds an .exe. A student should compare both tools on speed of execution, speed of development, error reporting and portability.

What earns the marks

• A compiler translates the entire source program into machine code in one go, producing an executable file that can be run without the translator present.
• An interpreter translates and executes the source program one statement at a time, so translation and execution are interleaved.
• A compiler reports all errors together after compilation, whereas an interpreter stops and reports the first error it encounters.
• Compiled code generally executes faster than interpreted code because translation has already happened.
• Interpreted code is generally quicker to develop and test because a program can be run immediately after editing, without a compile step.
• A compiled executable is platform-specific and must be recompiled for a different processor or operating system, while interpreted source can often run on any machine with a suitable interpreter.

Common mistakes and how to put them right

• Saying a compiler 'runs' the program.

  Put it right: Describe compilation as translation into machine code, then execution of that machine code.

• Claiming an interpreter translates the whole program first.

  Put it right: Link each translated statement to its immediate execution.

• Stating that compiled programs never have errors.

  Put it right: Distinguish syntax errors found at translation from logic errors found by testing.

Exam tips

• Use a comparison table with rows for translation method, execution speed, development speed and error reporting to keep the answer structured.
• Name a concrete example, such as a C compiler producing an executable or a Python interpreter running a script, to make each characteristic clear.
• When asked to recommend one tool, justify the choice using the context given, for example fast execution for a released game versus quick testing during development.