# Lecture 05: Lexical Analysis – Deterministic Finite Automaton

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what are the responsibilities of the lexical analyser
[1] tokenizing source [2] removing comments [3] saving text of identifiers, numbers, strings [4] saving source locations (file, line, column) for error messages
whata re the 3 ways to build a lexical analyser
(1) Write a formal description (e.g., REs) of the token patterns, a Design a state transition diagram (DFA) that describes the token patterns and (2) write a program to implement the diagram, or (3) write a table-driven implementation of DFA.
Whata re state transition diagrams?
directed graphs, are representation of mathematical “machines” called finite state automata (FSA) or just finite automata (FA).
Finite automata could be _____(DFA) or ______(NFA).
Finite automata could be deterministic (DFA) or nondeterministic (NFA).
when is FA determanistic?
A FA is deterministic if it performs the same operation (state transition) in a given situation (its current state and input).
when is fa nondeterministic
A FA is nondeterministic if it can perform any of a set of state transitions in a given situation.
what are the properties of a finite state automaton (FSA), or simply finite automaton
[1] read in' str' from L-R, 1 sym' at a time[2] in 1 of a finite No. ofState[3]4 each sym' it moves to a new state determined by its current state&the sym' read[4] str' is acptd or rejcted depending on the state of the machine after read the final sym'
what is the formal deffinition of finite automation (FA) M
finite set Q of states, finite alphabet Σ of input symbols, distinguished start state q1 ∈ Q, set of final states F ⊆ Q, and transition function δ: Q × Σ → Q that chooses a new state for M based on the current state, Q, and the current input symbol, Σ
what is DFA for Lexical Analysis
As far as lexical analysis is concerned, a DFA is a string processing machine
what does DFA do for Lexical Analysis
fuck you
what is The set of all strings accepted by a DFA known as
language recognised
how are DFA digrams simplified?
Similar to the case of REs, we name a set of symbols letter = {a, b, c,..., z, A, B, C,..., Z} digit = {0,...,9} and replace their arcs by a single arc labelled letter Or digit (or simply d as in our example)