RE to DFA by Direct Method (Compiler Design) | Example 2

Published: 26 March 2020
on channel: Easy Computer Engineering

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In this lecture, we convert a Regular Expression (RE) to a Deterministic Finite Automaton (DFA) using the Direct Method by computing Nullable, Firstpos, Lastpos, and Followpos functions. This method is based on syntax trees and is commonly used in Compiler Design.

🔹 What You’ll Learn:
✅ Understanding RE to DFA Conversion by Direct Method
🔸 How Regular Expressions are converted directly into DFA.
🔸 Why this method is efficient in Lexical Analysis of Compilers.
✅ Step-by-Step Process:
🔸 Step 1: Construct the Syntax Tree for the given Regular Expression.
🔸 Step 2: Compute the following functions:
🔹 Nullable – Determines if a node can be ε.
🔹 Firstpos – Identifies possible starting positions in syntax tree.
🔹 Lastpos – Identifies possible ending positions in syntax tree.
🔹 Followpos – Defines how positions relate in DFA state transitions.
🔸 Step 3: Using Followpos, construct the Transition Table.
🔸 Step 4: Design the DFA from Followpos Table.
✅ Example Walkthrough:
🔸 Full step-by-step example converting RE to DFA using Direct Method.
✅ Reference Book:
🔸 For more details, refer to "Compilers: Principles, Techniques, and Tools" by Aho, Lam, Ullman, Sethi.

📌 This video is perfect for students learning Compiler Design, Automata Theory, and Lexical Analysis.

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Using followpos we design DFA, for this you can refer book "Compilers" by Aho, Lam, Ullman, Sethi.
Also watch the Video RE to DFA by direct method example 1: • RE to DFA by Direct Method | Example 1 | ...

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