Found 146 Articles for Compiler Design

Yes, we can convert a NFA into DFA. For every NFA there exists an equivalent DFA. The equivalence is defined in terms of languages acceptance. Since NFA is nothing but a finite automata in which zero, one or more transitions on an input symbols are permitted. It can always construct finite automata which will simulate all moves of DFA on a particular input symbol in parallel, then get a finite automata in which there will be exactly one transition on every input symbol. Here, corresponding to a NFA there exist a DFA. To construct DFA equivalent to NFA, it should ... Read More

Non-Deterministic means that there can be several possible transitions on the same input symbol from some state. The output is non-deterministic for a given input. NFA can be represented as a nondeterministic finite state machine.NFA can be represented by 5 tuples (Q, $\sum$, $\delta$, q0, F)Q is a finite non-empty set of states.$\sum$ is a finite set of input symbols.$\delta$ is the transition function to move from the current state to the next state.∴ $\delta$:Q x $\sum$ → 2Qq0 ∈ Q is the initial state.F \subseteq Q is the set of final states.Example1 − Draw NFA for the Regular Expression ... Read More

Deterministic means that on each input there is one and only one state to which the automata can have the transition from its current state. In deterministic finite automata, the head can move only in one direction to scan the input tape symbols. But in the case of two-way, finite automata on scanning an input symbol the head of the tape may move in right or left from its current position.A deterministic finite automata is a set of 5 tuples and defined asM=(Q, Σ, $\delta$, q0, F) where, Q: A non-empty finite set of states present in the finite control ... Read More

A Regular Expression is a representation of Tokens. But, to recognize a token, it can need a token Recognizer, which is nothing but a Finite Automata (NFA). So, it can convert Regular Expression into NFA.Algorithm for the conversion of Regular Expression to NFAInput − A Regular Expression ROutput − NFA accepting language denoted by RMethodFor ε, NFA isFor a NFA isFor a + b, or a | b NFA isFor ab, NFA isFor a*, NFA isExample1 − Draw NFA for the Regular Expression a(a+b)*abSolutionExample2 − Draw NFA for a + b + abSolutionExample3 − Draw NFA for letter (letter+digit)*SolutionExample4 − ... Read More

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

Regular expressions are an important notation for defining patterns. Each pattern connects a set of strings. Therefore regular expressions will give as names for sets of strings.It supports an appropriate and useful notation for describing tokens. Regular Expressions define the language accepted by finite Automata (Transition Diagram).Regular Expressions are defined over an alphabet $\sum$.If R is a Regular Expression, therefore L(R) represents language denoted by the regular expression.Language − It is a collection of strings over some fixed alphabet. The empty string can be indicated by ε.Example − If L (Language) = set of strings of 0’s & 1’s of ... 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

Lexical Analysis is the first step of the compiler which reads the source code one character at a time and transforms it into an array of tokens.Token − The token is a meaningful collection of characters in a program. These tokens can be keywords including do, if, while etc. and identifiers including x, num, count, etc. and operator symbols including >, >=, +, etc., and punctuation symbols including parenthesis or commas. The output of the lexical analyzer phase passes to the next phase called syntax analyzer or parser.Example − A statement a = b + 5 will have the tokens.Role ... Read More