📘 1. Syntax Analysis (Parsing)

✅ Definition

Syntax Analysis is the second phase of a compiler in which the sequence of tokens (from lexical analysis) is checked according to the grammar rules of the language.

👉 It determines whether the program is syntactically correct or not.

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🔄 Position in Compiler

Source Code → Lexical Analyzer → Syntax Analyzer → Semantic Analyzer

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📊 Basic Working

• Input → Tokens from lexical analyzer
• Output → Parse Tree / Syntax Tree

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📌 Example

Input Tokens:

int x = 10 ;

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Valid Statement ✅

Follows grammar rules

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Invalid Statement ❌

int = x 10 ;

👉 Parser detects syntax error

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⭐ Key Points (Exam)

👉 Checks grammar rules (CFG) 👉 Generates parse tree 👉 Detects syntax errors

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🧠 2. Role of the Parser

✅ Definition

A Parser is a program that performs syntax analysis by taking tokens as input and producing a parse tree.

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🔧 Main Functions of Parser

1. Check Syntax

• Verifies whether input follows grammar rules

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2. Build Parse Tree

• Represents structure of program

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3. Report Errors

• Detects and reports syntax errors

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4. Interface with Other Phases

• Takes tokens from lexical analyzer
• Sends parse tree to semantic analyzer

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📊 Role Diagram

Tokens → [Parser] → Parse Tree → Semantic Analysis

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🌳 3. Parse Tree (Reminder)

• Root → Start symbol
• Leaves → Tokens
• Shows hierarchical structure

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📌 Example

a + b * c

Parse tree ensures:

a + (b * c)

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⚠️ 4. Syntax Errors

✅ Definition

Errors that occur when input does not follow grammar rules.

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📌 Examples

Error Type	Example
Missing symbol	int x = 10 (missing ;)
Wrong order	int = x 10;
Unbalanced brackets	(a + b

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⭐ Key Point (Exam)

👉 Parser must detect and recover from errors

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🔄 5. Types of Parsing

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🔹 1. Top-Down Parsing

• Starts from start symbol
• Builds parse tree from root to leaves

👉 Example:

• Recursive Descent Parser
• LL(1) Parser

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🔹 2. Bottom-Up Parsing

• Starts from input string
• Builds parse tree from leaves to root

👉 Example:

• Shift-Reduce Parser
• LR Parser

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📊 Comparison

Feature	Top-Down	Bottom-Up
Direction	Root → Leaves	Leaves → Root
Approach	Predictive	Reduction
Complexity	Simple	Complex
Example	LL(1)	LR

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🧪 6. Example (Parsing Process)

Grammar:

E → E + T | T
T → id

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Input:

id + id

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Steps:

1. Parser reads tokens
2. Matches with grammar rules
3. Builds parse tree
4. Confirms validity

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🎯 7. Error Handling in Parsing

🔧 Techniques (Basic Idea)

• Panic mode recovery
• Phrase-level recovery

👉 Ensures compilation continues even after errors

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🎯 8. Important Exam Concepts

👉 Frequently asked:

• Define syntax analysis
• Role of parser
• Types of parsing
• Syntax errors with examples
• Difference between top-down and bottom-up
• Draw parsing process diagram

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📝 9. Short Notes (Quick Revision)

Syntax Analysis

• Second compiler phase
• Checks grammar rules

Parser

• Builds parse tree
• Detects errors

Parsing Types

• Top-down
• Bottom-up

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📊 10. Final Summary Table

Aspect	Syntax Analysis	Parser
Definition	Checks syntax of tokens	Program that performs parsing
Input	Tokens	Tokens
Output	Parse tree	Parse tree
Function	Validate structure	Build tree & detect errors
Errors	Syntax errors	Reports errors
Importance	Very High	Very High

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✅ Final Conclusion

• Syntax Analysis ensures the program follows correct grammar
• The Parser is the core component that performs this task
• It builds the parse tree and detects errors
• Essential for further phases like semantic analysis

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