An automata is an abstract model of digital computers with discrete inputs and outputs. Every automata include a mechanism for reading inputs. It is considered that input is a string over a given alphabet, written on an input file that the automata can read. The input file is divided into smaller parts known as cells.It is a Machine or a Recognizer for a language that is used to check whether a language accepts the string or not. In Finite Automata, Finite means a finite number of states and Automata means the Automatic Machine which works without any interference of human ... Read More

The language accepted by finite automata can be simply defined by simple expressions known as Regular Expressions. It is an effective approach to describe any language. A regular expression can also be represented as a sequence of patterns that represent a string. Regular expressions are used to connect character sequence in strings. The string searching algorithm used this pattern to discover the operations on a string.There are various rules for regular expressions which are as follows −ε is a Regular expression.Union of two Regular Expressions R1 and R2.i.e., R1 + R2 or R1|R2 is also a regular expression.Concatenation of two ... Read More

Lexical Analysis can be designed using Transition Diagrams.Finite Automata (Transition Diagram) − A Directed Graph or flowchart used to recognize token.The transition Diagram has two parts −States − It is represented by circles.Edges − States are connected by Edges Arrows.Example − Draw Transition Diagram for "if" keyword.To recognize Token ("if"), Lexical Analysis has to read also the next character after "f". Depending upon the next character, it will judge whether the "if" keyword or something else is.So, Blank space after "if" determines that "If" is a keyword."*" on Final State 3 means Retract, i.e., control will again come to previous ... Read More

Lexical Analysis has to access secondary memory each time to identify tokens. It is time-consuming and costly. So, the input strings are stored into a buffer and then scanned by Lexical Analysis.Lexical Analysis scans input string from left to right one character at a time to identify tokens. It uses two pointers to scan tokens −Begin Pointer (bptr) − It points to the beginning of the string to be read.Look Ahead Pointer (lptr) − It moves ahead to search for the end of the token.Example − For statement int a, b;Both pointers start at the beginning of the string, which ... Read More

A compiler is a computer program that converts source code written in a computer language (the source language) into another computer language (the target language, providing having a binary form referred to as object code). The best reason for inadequate to convert source code is to create an executable code.The compiler is generally used for programs that translate source code from a high-level programming language to a lower-level language (e.g., assembly language or machine code). A program that translates from a low-level language to a higher level one is a decompiler.A program that translates between high-level languages is generally known ... Read More

It is an approach for making a self-compiling compiler that is a compiler written in the source programming language that it determine to compile. A bootstrap compiler can compile the compiler and thus you can use this compiled compiler to compile everything else and the future versions of itself.Uses of BootstrappingThere are various uses of bootstrapping which are as follows −It can allow new programming languages and compilers to be developed starting from actual ones.It allows new features to be combined with a programming language and its compiler.It also allows new optimizations to be added to compilers.It allows languages and ... Read More

Macro-ProcessorsMany assembly languages support a “macro” facility whereby a macro statement will translate into a sequence of assembly language statements and possibly other macro statements before being translated into a machine program. Therefore, a macro facility is a text replacement capability.It can illustrate the utility of macros, consider a situation in which a machine does not have a single machine or assembly language statement that adds the contents of one memory address to another as hypothetical assembly instruction ADD X, Y. Instead, suppose the machine has an instruction LOAD, which moves a datum from memory to a register, an instruction ... Read More

Detection and reporting of errors in the source program is the main function of the compiler. An error can occur at any phase of compilation. A good compiler must determine the line number of the program exactly, where the errors have occurred. Various errors that can occur at a different level of compilation are as follows −The first of these are lexical (scanner) errors − Some of the most common types here consist of illegal or unrecognized characters, mainly, caused by typing errors. A common way for this to happen is for the programmer to type a character that is ... Read More

Imperative LanguagesImperative languages are those which facilitate the computation by mean of state changes. By a state, it means the condition of a computer’s random access memory (RAM) or storage. It is helpful to think of computer memory as a sequence of snapshots, each one capturing the values in all memory cells at a particular time. Each snapshot records a state.When a program is entered, associated data exists in a certain condition, say an unsorted list off-line. It is the programmer’s job to specify a sequence of changes to the store that will produce the desired final state, perhaps a ... Read More

Procedural LanguagesProcedural languages are command-driven or statement-oriented languages. A program includes a sequence of statements, and the implementation of each statement generates the interpreter to modify the value of one or more areas in its memory that enters a new state.The format of procedural languages arestatement1;statement2;C, Pascal, FORTRAN, and equivalent languages are procedural languages. Each statement in the language communicates the computer to do something. A program in a procedural language is a list of instructions. For very small programs, no other arranging principle is required. Such language includes a sequence of procedures that execute when called. Each procedure includes ... Read More