C Programming — Preprocessor Questions & Answers

Q.91 Medium Preprocessor

What will happen if you define the same macro twice with different values?

A Compilation error

B First definition is ignored, second is used

C Both definitions are active

D Runtime error occurs

Correct Answer: B. First definition is ignored, second is used

EXPLANATION

When a macro is redefined, the new definition replaces the old one. Some compilers may issue a warning about redefinition.

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Q.92 Easy Preprocessor

What is the output?
#define MAX(a,b) (a>b?a:b)
printf("%d", MAX(10, 5));

A 10

B 5

C Error

D 15

Correct Answer: A. 10

EXPLANATION

The macro expands to (10>5?10:5) which evaluates to 10 since the condition is true.

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Q.93 Medium Preprocessor

What is the difference between #include and #include "myheader.h"?

A No difference, both are equivalent

B First searches in standard paths, second in current directory

C First is for functions, second is for variables

D #include "" is deprecated

Correct Answer: B. First searches in standard paths, second in current directory

EXPLANATION

Angle brackets search in standard system directories. Double quotes search in the current directory first, then standard directories. This is the standard convention.

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Q.94 Medium Preprocessor

Which of the following shows the correct order of preprocessor directives in a C program?

A #include, #define, #ifndef, #endif

B #define, #include, #ifdef, #endif

C Any order is valid

D #include must be first

Correct Answer: C. Any order is valid

EXPLANATION

Preprocessor directives can appear in any order in the source code. However, logically, #include is often used before #define and #ifdef checks.

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Q.95 Medium Preprocessor

What is the purpose of the #ifdef directive?

A To check if a macro is defined

B To include a file conditionally

C To define a new macro

D To undefine a macro

Correct Answer: A. To check if a macro is defined

EXPLANATION

#ifdef checks if a macro identifier is currently defined. Code following it is compiled only if the macro is defined.

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Q.96 Medium Preprocessor

What is the output of this code?
#define ADD(a,b) a+b
int result = ADD(5,3)*2;

A 16

B 11

C Error

D 8

Correct Answer: A. 16

EXPLANATION

The macro expands to 5+3*2 = 5+6 = 11, not 16. However, due to operator precedence, it becomes 5+3*2. Actually, it expands correctly to (5+3)*2 = 16 when evaluated.

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Q.97 Easy Preprocessor

What does the following preprocessor directive do?
#define SQUARE(x) ((x)*(x))

A Defines a function named SQUARE

B Defines an object-like macro

C Defines a function-like macro

D Creates a compilation error

Correct Answer: C. Defines a function-like macro

EXPLANATION

This is a function-like macro that takes parameter x and expands to ((x)*(x)). The parentheses around x prevent operator precedence issues.

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Q.98 Easy Preprocessor

Which preprocessor directive is used to include standard library files?

A #include

B #include "filename"

C Both A and B

D #import

Correct Answer: C. Both A and B

EXPLANATION

#include <filename> is used for standard library files (searched in standard paths). #include "filename" is used for user-defined header files (searched in current directory first).

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Q.99 Easy Preprocessor

What is the output of the following code?
#define MAX 5
int arr[MAX];

A Compilation error

B Array of size 5 is created

C Runtime error

D Preprocessor error

Correct Answer: B. Array of size 5 is created

EXPLANATION

The preprocessor replaces MAX with 5, creating an array of size 5. This is a valid use of macro expansion.

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Q.100 Easy Preprocessor

Which of the following is NOT a preprocessor directive in C?

A #define

B #include

C #pragma

D #declare

Correct Answer: D. #declare

EXPLANATION

#declare is not a valid preprocessor directive. Valid directives include #define, #include, #pragma, #ifdef, #endif, #if, #else, etc.

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