Discuss different types of common programming errors.

Types of Common Programming Errors

When a program is written, errors are often unavoidable, no matter how careful the programmer is. These errors may occur during:

• Lexical analysis
• Syntax analysis
• Semantic analysis
• Or even during execution

Below are the four main types of programming errors typically encountered in compiler design:

1. Lexical Errors

These are errors in the spelling or format of tokens during lexical analysis.

Examples:

• Misspelling a keyword or identifier:
  • Typing elipseSize instead of ellipseSize
• Using invalid or missing characters:
  • "Hello (missing closing quote for a string)
  • $value (invalid character in variable name)

Detected by:

Lexical analyzer

2. Syntactic Errors

These errors violate the grammar rules of the programming language.

Examples:

• Missing or extra semicolons, brackets, braces:
• 
• case used without a switch:
• 
  

3. Semantic Errors

These are meaning-related errors – the code is syntactically correct but makes no sense logically.

Examples:

• Type mismatch:

• Returning a value in a void function:

Detected by:

Semantic analyzer

4. Logical Errors

These are hardest to detect because the code is syntactically and semantically valid, but it doesn’t do what the programmer intended.

Examples:

• Using = (assignment) instead of == (comparison):

• Incorrect use of loops or conditions that cause wrong output or infinite loops.

Detected by:

Usually caught only during testing or debugging

Error Detection & Recovery Goals

The compiler’s error handler aims to:

1. Clearly report the location and type of error
2. Recover quickly so that it can detect more errors later
3. Add minimal overhead to the compilation of correct code

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Summary Table

Type of Error	Description	Example	Detected By
Lexical Error	Mistakes in spelling of tokens	elipseSize, "Hello	Lexical Analyzer
Syntax Error	Structure/grammar violations	Missing ;, case without switch	Parser
Semantic Error	Type mismatches, invalid returns	return 5; in void method	Semantic Analyzer
Logical Error	Code runs, but logic is flawed	if (x = 5) instead of x == 5	Testing/Debugging