In the C programming language, which of the following is not a valid representation of a real (floating-point) constant?
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A426
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B321.0
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C-621.231
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D+201.2314
Answer
Correct Answer: 426
Explanation
Introduction:This question distinguishes integer constants from floating-point (real) constants in C. Understanding literal forms helps prevent unintended type choices and implicit conversions.
Given Data / Assumptions:
- Options include an integer-looking token (426) and classic decimal forms with optional signs.
- Context: C numeric literal grammar for floating constants.
Concept / Approach:
In C, a floating (real) constant typically has a decimal point and/or an exponent part (e.g., 1.0, .5, 2e3, -3.14, +6.02e23). An integer constant lacks a decimal point and exponent (e.g., 426) and therefore is not a real constant. A leading plus or minus is a unary operator applied to the literal token; it does not invalidate the floating form.
Step-by-Step Solution:
Step 1: Inspect '321.0' — decimal point present, valid floating literal.Step 2: Inspect '-621.231' — unary minus with decimal, valid floating literal.Step 3: Inspect '+201.2314' — unary plus with decimal, valid floating literal.Step 4: Inspect '426' — no decimal point or exponent, thus an integer literal, not a real constant.Verification / Alternative check:
Compilers will type '426' as an int by default, whereas literals with a decimal point are typed as double unless suffixed (e.g., f/F for float).
Why Other Options Are Wrong:
All other options contain a decimal point and thus are valid real constants in C.
Common Pitfalls:
Confusing the presence of a sign with type; forgetting exponent notation also creates real constants (e.g., 1e2).
Final Answer:
426