Question

Which of the following is invalid floating point constant?

• A. \(0.65e4\)
• B. \(1.5e+5\)
• C. \(18E+3.5\)
• D. \(-1.2E-1\)

Hint:

In exponential notation, the exponent must always be an integer. Examples: \(2.5E3\), \(1.4E-2\), \(5e+7\) are valid, but \(2.5E3.5\) is invalid.

Answer 1

The Correct Option is C

Concept: In C programming, a floating-point constant may be written in exponential notation as: \[ m \times 10^e \] where:
• \(m\) is the mantissa.
• \(e\) is an integer exponent.
• The exponent is written after \(E\) or \(e\). General format: \[ \text{mantissa}E\text{exponent} \] The exponent must always be an integer value.

Step 1: Check Option (A).
\[ 0.65e4 \] means \[ 0.65\times10^4 \] The exponent \(4\) is an integer. Hence this is valid.

Step 2: Check Option (B).
\[ 1.5e+5 \] means \[ 1.5\times10^5 \] Again the exponent is an integer. Hence this is valid.

Step 3: Check Option (C).
\[ 18E+3.5 \] Here the exponent is \[ 3.5 \] which is not an integer. Floating-point constants do not allow fractional exponents. Therefore this representation is invalid.

Step 4: Check Option (D).
\[ -1.2E-1 \] means \[ -1.2\times10^{-1} \] which is perfectly valid.

Step 5: Write the final answer.
Hence the invalid floating-point constant is \[ \boxed{18E+3.5} \] Therefore option (C) is correct.