In programming language translation, what is the main difference between a compiler and an interpreter in how they execute a program?

Introduction / Context:
When you write a program in a high level language such as C, Java, or Python, the code that you type is not directly executed by the hardware. There must be a translation step that converts human readable source code into machine instructions that the CPU can understand. Two classic approaches to this translation are compilation and interpretation. Understanding how a compiler and an interpreter differ is a very common exam topic in operating systems and programming language theory.

Given Data / Assumptions:

• We have a high level source program written in a language like C or Python.
• A compiler or interpreter is available for that language.
• The goal is to run the program on a specific computer system.

Concept / Approach:
A compiler reads the entire source program, checks it for errors, and translates it into an equivalent target program, usually machine code or an intermediate representation such as bytecode. This translation happens before the program is run. Once the compiled program is produced, it can be executed many times without recompilation. An interpreter, in contrast, reads the source program and executes it step by step, often line by line or statement by statement. It translates each construct just before or as it is executed, without producing a separate machine code file in advance. Because of this, compiled programs often run faster at runtime, while interpreted programs can be easier to test and debug.

Step-by-Step Solution:
Step 1: Recall that a compiler performs translation ahead of time and produces a separate executable or bytecode file.Step 2: Recall that an interpreter reads the source, analyses each statement, and executes it immediately without generating a permanent executable.Step 3: Compare the options and identify which one correctly states this difference in timing and execution style.Step 4: Option A clearly says that a compiler translates the entire program first and that an interpreter works line by line at runtime.Step 5: The other options talk about behaviour that does not match standard definitions, so option A is correct.

Verification / Alternative check:
Classic examples support this definition. C and C plus plus are usually compiled languages where the compiler generates an executable file. Python and many shell languages are commonly interpreted, where the interpreter reads and executes scripts directly. Some modern systems blend both ideas with just in time compilation, but the basic conceptual difference remains the same in introductory theory.

Why Other Options Are Wrong:
Option B claims that a compiler executes each line directly on the CPU and that an interpreter always generates an executable first, which reverses their normal roles.Option C states that neither translates source code, which is clearly false since translation is their main purpose.Option D misclassifies the usage domains of compilers and interpreters; in practice, both approaches are used for many types of languages.

Common Pitfalls:
Students often think that a language is either compiled or interpreted in an absolute sense. In reality, many languages have both compilers and interpreters. The question is about the behaviour of the tools, not about specific languages. Another pitfall is to forget that compilers work ahead of time while interpreters work during execution.

Final Answer:
The correct answer is A compiler translates the entire source program into machine code before execution, while an interpreter translates and executes the program line by line at runtime.