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GO Classes DPP | GATE CS | C Programming | Macro Expansion Trap

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11 11 votes

Consider the statement:

double ans = 18.0 / squared(2 + 1);

For each of the following macro definitions, find the value of $\texttt{ans}$.

#define squared(x) x*x
#define squared(x) (x*x)
#define squared(x) (x)*(x)
#define squared(x) ((x)*(x))

Which option gives the correct values in order?

  1. $\texttt{12, 3.6, 18, 2}$
     
  2. $\texttt{2, 2, 2, 2}$
     
  3. $\texttt{12, 12, 18, 2}$
     
  4. $\texttt{18, 3.6, 18, 2}$

4 Answers

1 1 vote

For:

$\texttt{#define squared(x) x*x}$

The statement becomes:

$\texttt{18.0 / 2 + 1 * 2 + 1}$

So:

$\texttt{9 + 2 + 1 = 12}$

 

For:

$\texttt{#define squared(x) (x*x)}$

The statement becomes:

$\texttt{18.0 / (2 + 1 * 2 + 1)}$

So:

$\texttt{18 / 5 = 3.6}$

 

For:

$\texttt{#define squared(x) (x)*(x)}$

The statement becomes:

$\texttt{18.0 / (2 + 1) * (2 + 1)}$

So:

$\texttt{6 * 3 = 18}$

 

For:

$\texttt{#define squared(x) ((x)*(x))}$

The statement becomes:

$\texttt{18.0 / ((2 + 1) * (2 + 1))}$

So:

$\texttt{18 / 9 = 2}$


Answer: A

0 0 votes
  1. #define squared(x) x*x → 12
  2. #define squared(x) (x*x) → 3.6
  3. #define squared(x) (x)*(x) → 18
  4. #define squared(x) ((x)*(x)) → 2

Final answer: 12, 3.6, 18, 2

option = A

 

 

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