Understand how an interpreter differs from a compiler in the way it…

The idea

A compiler translates the whole high-level source program in one go, producing a machine code file that can then be run without the compiler present. Errors are reported together after translation, and the compiled program usually runs quickly because translation has already happened. An interpreter translates and executes the source one statement at a time, so it stops at the first error it meets and no separate machine code file is produced; the interpreter must be present each time the program runs. Interpretation suits development and testing because errors are found immediately, while compilation suits finished software that must run efficiently and be distributed without source code.

What earns the marks

• A compiler translates the entire source program before any of it is executed, producing a machine code file.
• A compiler reports errors together after translating the whole program, so several errors may be listed at once.
• An interpreter translates and executes one statement at a time, stopping when it reaches an error.
• An interpreter does not produce a standalone machine code file, so the interpreter must be available whenever the program runs.
• Compiled code generally executes faster because translation is completed in advance; interpreted code is convenient during development because errors appear immediately.
• The choice depends on purpose: interpretation for testing and learning, compilation for efficient distribution of finished software.

Common mistakes and how to put them right

• Saying an interpreter translates the whole program first.

  Put it right: It works statement by statement, executing as it goes.

• Claiming a compiler runs the program.

  Put it right: The compiler produces machine code, and the resulting file is what runs.

• Thinking interpreted programs never become machine code.

  Put it right: Each statement is translated into machine code as it is reached, but no complete machine code file is saved.

• Believing only compilers find errors.

  Put it right: Both find errors, but a compiler reports them after translating everything, while an interpreter stops at the first error encountered.

Exam tips

• Answer with the translation unit: whole program for a compiler, one statement at a time for an interpreter.
• Mention the output: a compiler produces a machine code file, an interpreter does not.
• Add the practical consequence, such as speed of the finished program or immediate error reporting, to secure the explanation mark.