C/C++ declarations: Which among the following lines are declarations (not definitions) — 1) extern int x; 2) float square(float x) { /* ... / } 3) double pow(double, double);

Introduction / Context:Correctly distinguishing between declarations and definitions shapes how you structure headers and source files. Declarations introduce names and types; definitions allocate storage or provide function bodies. This question asks you to classify three common patterns you will encounter in real projects.

Given Data / Assumptions:

• 1) 'extern int x;'
• 2) 'float square(float x) { / body */ }'
• 3) 'double pow(double, double);'
• Standard C/C++ rules apply.

Concept / Approach:

• For objects: 'extern' declares without defining (no storage).
• For functions: a prototype with a semicolon is a declaration; a body enclosed in braces is a definition.
• Therefore, 1 and 3 are declarations; 2 is a definition.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 2: Contains a body; it is a definition, not a mere declaration.
• Single-choice options miss that two items are declarations.

Common Pitfalls:

• Putting definitions in headers can cause multiple-definition errors.
• Forgetting that functions always have external linkage by default unless qualified (e.g., 'static').

Final Answer: