A compiler is a program that translates code written in a high-level programming language into machine code

1. Compiler Design - Lecture 1
Introduction to Compiler
Stage 3 - Computer Science
Department

2. What is a Compiler?
• • A compiler is a program that translates code
written in a high-level programming language
into machine code.
• • It allows programmers to write in human-
readable languages while enabling the
computer to execute the instructions.
• • Example: Translating C++ code into Assembly
or Machine Code.

3. Why Do We Need a Compiler?
• • Computers only understand binary (0s and
1s).
• • Writing in machine code is complex and
error-prone.
• • Compilers make programming easier,
efficient, and portable.
• • Provide error detection (syntax/semantic
errors) and optimizations.

4. Phases of a Compiler
• 1. Lexical Analysis
• 2. Syntax Analysis
• 3. Semantic Analysis
• 4. Intermediate Code Generation
• 5. Code Optimization
• 6. Code Generation

5. Example: int a = b + 5;
• • Lexical Analysis → Tokens: [int], [a], [=], [b],
[+], [5], [;]
• • Syntax Analysis → Valid assignment
expression
• • Semantic Analysis → Checks types of
variables
• • Intermediate Code → t1 = b + 5; a = t1
• • Optimization → a = b + 5
• • Code Generation → Assembly instructions

6. Syntax vs Logical Errors
• • Syntax Error: Missing semicolon in C code.
• Example: int x = 5 // Error
• • Logical Error: Program compiles but gives
wrong results.
• Example: Division by zero (int z = x / 0;)

7. Thinking Question
• Imagine if compilers did not exist:
• • How would programmers write code?
• • Would programming be practical using only
0s and 1s?
• • Discuss the importance of compilers in
software development.