What is Compiler: Working and Types

What is Compiler: Working and Types

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Jaya Sharma
Senior Executive Content
Updated on Dec 4, 2023 18:38 IST

Compiler is a type of computer program for developers that translates high-level source code into machine code or an intermediate language, enabling the creation of executable programs. Let’s understand more about it.


A compiler is a special program that translates source code written in one programming language (like Python, C, or Java) into another language, usually a lower-level language like machine code or an intermediate language.

Table of Contents

What is Compiler?

A compiler is a software tool for converting human-written computer code into machine code. It performs several tasks, such as flow control, error detection, syntax analysis, optimization, and type checking. The main purpose of a computer is to ensure that the source code is well-structured and the program is easy to understand. It ensures that the generated machine code is correct and optimized for the hardware being used. 

The compiler changes a program written in one language without altering the meaning of a program. Whenever you implement a program written in HLL programming language, it implements it into two parts. For the first element, the source code is compiled and translated into an object code. The object program is translated into target code through an assembler in the second element.

How Does a Compiler Work?

The following steps are the phases of compiler that are undertaken by it in order to convert the code to output:

  1. Lexical analysis: It is the first phase where high-level input program is converted into a sequence of tokens. This can be implemented with Deterministic finite Automata. The output is the sequence of tokens that are sent to the parser for syntax analysis.
  2. Syntax Analysis/ Parsing: It is the second phase of a compiler. In this phase, it verifies the syntactical structure of a given input. To do so, it builds a data structure called Syntax or Parse tree. The parse tree is constructed using pre-defined grammer of language and input string. If a given input string can be produced using syntax tree, the input string is found to be in the correct syntax. If it is not correct, the error is reported by syntax analyzer.  
  3. Semantic analysis: It is the process of interpreting meaning from text. This allows the computer system to understand and interpret paragraphs, sentences and whole documents. For this purpose, it analyzes the grammatical structure and identifies relationships between individual words.
  4. Intermediate code generation: It can translate source program into machine program. An intermediate code is generated because the compiler cannot directly generate machine code in one pass. It first converts the source program into intermediate code to perform efficient generation of machine code. It is represented in postfix notation, directed acyclic graph, quadruples, and triples.
  5. Code optimization: It is a program transformation technique. The aim of this phase of compiler is to code improvement by enabling it to consume fewer resources and deliver high speed. High-level language constructs are replaced with efficient low-level programming codes. For increasing the speed of a program, unnecessary code strings are eliminated and a sequence of statements are organized. 
  6. Code Generation: It is the final compilation phase. The generated code is an object code of lower-level programming languages such as assembly language. Source code written in higher-level language is converted into a lower-level language that results in lower-level object code. 

Let us learn about the phases of the compiler as well:


Compiler Structure


The Three-Stage Compiler Structure simplifies the compiler’s structure by dividing it into three stages: Front End, Middle End, and Back End. Each stage serves a distinct purpose in the compilation process. Here’s an overview of the Three-Stage Compiler Structure:

Front End:

  • Input: The source code written in a high-level programming language.
  • Tasks:
    • Lexical Analysis (Scanning): The front-end includes a lexer (lexical analyzer) that scans the source code and breaks it down into tokens (basic units like keywords, identifiers, operators).
    • Syntax Analysis (Parsing): A parser analyzes the syntactic structure of the code based on a formal grammar and generates a parse tree or abstract syntax tree (AST) representing the program’s structure.
    • Semantic Analysis: The front end performs initial semantic checks, such as type checking and scope resolution, and may generate an annotated parse tree or AST.
    • Output: An AST or annotated parse tree.

Middle End:

  • Input: The AST or annotated parse tree generated by the front end.
  • Tasks:
    • Intermediate Code Generation: The middle end produces an intermediate representation (IR) of the source code. This IR is closer to machine code but is still abstract and platform-independent.
    • Optimization: Optimizations are applied to the intermediate code to improve program efficiency. These optimizations may include constant folding, loop optimization, and dead code elimination.
    • Output: Optimized intermediate code.

Back End:

  • Input: The optimized intermediate code generated by the middle end.
  • Tasks:
    • Code Generation: The back end translates the intermediate code into target machine code or another lower-level language. It involves mapping high-level language constructs to specific machine instructions.
    • Register Allocation: Assigns variables and values to processor registers efficiently for optimal performance.
    • Instruction Selection: Chooses the appropriate machine instructions to implement the operations specified in the intermediate code.
    • Output: Target machine code or lower-level code.

Types of Compiler

The following are the different types of compilers that are used:

  1. Just-in-time (JIT) compiler: It compiles programs as they are executed. It is faster than traditional compilers and helps in reducing program size by elimination of redundant code. This reduced the size of the program and make it more efficient. This helps in performance improvement. 
  2. Cross compiler: This is a technology to allow developers to compile and run codes on various platforms. This type is useful while working on several versions of code for ensuring that all platforms are being supported. This is useful while working on a new platform to verify whether the code is working on this platform. 
  3. Bytecode compiler: It translates high-level language into machine code which is executable on target machine. Such compilers allow developers to write codes in a high-level language and compile them into machine code. Through this compiler, developers write concise and comprehensible codes. These compilers should be written in high-level language. They are not suitable for developing low-level code.
  4. Source-to-source compiler: This software tool translates the source code into executable code. Such compilers are used to translate source code written in multiple programming languages. The translation process can be completed in both manual and automatic methods. Compilers translate source code into machine code which is executed by a target machine.
  5. Binary compiler: This compiler translates the source code file into binary format. This type of format stores the program information in a compact form that is easily read by computer. Developers use compilers for network programming, database administration, and web development.
  6. Hardware compiler: Such compilers compile the source code into machine code for transforming source code into machine code. Post that, the computer executes this code. Such compilers are used in operating systems, embedded systems, and computer games. Assembler is a type of hardware compiler.

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Advantages of Compiler

The following are the advantages of compilers:

  • Compilers are more efficient in comparison with interpreters since they produce machine code which is more optimized for the hardware platform on which it will be run.
  • They perform comprehensive error checks during the compilation process. It helps in detecting semantic, logical and syntax-related errors within the code before it is run.
  • After the compilation of a program, it is possible to run the resulting machine code on any device having an appropriate operating system or hardware.
  • The compiler optimizes generated machine code by eliminating any redundant instructions and by rearranging the code.

Disadvantages of Compiler

The following are the disadvantages of compilers:

  • It is more difficult to debug a compiled code than an interpreted code since the generated machine code is not easy to understand or read.
  • These are less interactive than interactive programs since they must be compiled before running. This slows down the process of development and testing.
  • The process of developing a compiler is complex and takes time. For this purpose, developers must be technically aware of the programming language and target hardware platform.
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Thus, compilers play a foundational role in the vast world of software development, enabling developers to communicate with machines effectively and produce efficient, executable programs across diverse platforms. Keep learning, Keep exploring!


Can a compiler handle multiple programming languages?

Some compilers are designed to handle multiple programming languages, while others are specific to a particular language. The ability to handle multiple languages depends on the design and capabilities of the compiler.

Are compilers and interpreters the same thing?

No, compilers and interpreters are different. Compilers translate the entire source code into machine code or bytecode before execution, while interpreters execute the code line by line without creating a separate compiled output. However, some languages use a combination of both compilation and interpretation techniques.

Are compilers language-specific?

Yes, compilers are typically designed for specific programming languages. Each programming language has its own syntax and semantics, requiring a compiler tailored to understand and translate that language's specific features.

Are there open-source compilers available?

Yes, there are many open-source compilers available for various programming languages. Examples include GCC (GNU Compiler Collection) for C, C++, and other languages, and LLVM (Low-Level Virtual Machine) compiler infrastructure, which supports multiple languages.

What is compiling in C?

Compiling in C involves translating human-readable C code into a format that a computer can execute. Basically, it translates the code into machine-executable code.

About the Author
Jaya Sharma
Senior Executive Content

Jaya is a writer with an experience of over 5 years in content creation and marketing. Her writing style is versatile since she likes to write as per the requirement of the domain. She has worked on Technology, Fina... Read Full Bio