Describe what a compiler does with a program's source code.

A compiler is a computer program that translates source code written in a high-level programming language (e.g., Java, C++, Python, etc.) into a lower level-code, usually in the form of machine code, assembly language, or bytecode. This compiled code can then be executed by a computer's hardware or virtual machine.

The main purpose of a compiler is to make it easier for humans to create programs that can be understood and executed by computers. High-level programming languages are designed to be more human-readable and closer to natural languages, while machine languages are composed of binary instructions that a computer's hardware can execute directly. A compiler acts as a bridge between these two, allowing programmers to write code in a more accessible language, which is then translated into a form that the computer can understand and execute.

Compiling a program's source code typically involves several steps: 1. Lexical analysis: The compiler scans the source code and breaks it down into tokens that represent keywords, identifiers, literals, operators, etc. 2. Syntax analysis: The compiler checks the tokens to make sure the code follows the proper syntax of the programming language. 3. Semantic analysis: The compiler checks the code for semantic errors (e.g., ensuring variables are declared before being used) and generates a syntax tree or abstract syntax tree (AST). 4. Intermediate code generation: The compiler translates the AST into an intermediate language, such as bytecode or assembly. 5. Code optimization: The compiler optimizes the intermediate code to improve the program's efficiency, such as removing unnecessary instructions or combining expressions. 6. Target code generation: The compiler translates the optimized intermediate code into the target language, such as machine code or assembly language that can be executed by the computer's hardware or virtual machine.

The compiler's task is often followed by a linking process, which combines one or more compiled object files together to produce the final executable program. The linker resolves references to external libraries, resolving symbols and addresses, and builds the resulting executable binary that can be run on the target platform. In conclusion, a compiler takes a program's source code written in a high-level programming language and translates it step by step into machine-executable instructions, making it easier for programmers to write code in a more human-readable form that a computer can understand and execute.