Compiler Design

Step 1: Understanding declarations.
Declarations specify variables, data types, and storage requirements but do not perform any computation or action at runtime.
Step 2: Comparison with other statements.
Assignment statements generate code to store values. Input/output statements generate code for data transfer. Control statements generate branching or looping code.
Step 3: Effect of declarations during compilation.
Declarations mainly affect symbol tables and memory allocation but do not result in executable instructions.
Step 4: Final conclusion.
Therefore, declarations usually produce no executable code when compiled.

Step 1: Understanding type checking.
Type checking ensures that operations in a program are applied to compatible data types, such as preventing addition of an integer and a string.
Step 2: Role of compiler phases.
Lexical analysis identifies tokens, while syntax analysis checks grammatical structure. Neither phase checks semantic correctness like type compatibility.
Step 3: Syntax-directed translation.
Type checking is part of semantic analysis, which is implemented using syntax-directed translation with attributes attached to grammar symbols.
Step 4: Final conclusion.
Hence, type checking is normally performed during syntax-directed translation.

Step 1: Understanding the role of a lexical analyzer.
The lexical analyzer (also called scanner) is the first phase of a compiler. It reads the source program as a sequence of characters.
Step 2: Identifying its main task.
Its primary function is to group characters into meaningful units called tokens, such as identifiers, keywords, operators, and literals.
Step 3: Output produced by lexical analysis.
After scanning the input, the lexical analyzer outputs a sequence (stream) of tokens, which is then passed to the syntax analyzer (parser).
Step 4: Final conclusion.
Hence, the correct output of a lexical analyzer is a stream of tokens.