MCQs on Preprocessor Directives | C Programming

Macros and #define

1. What is the primary purpose of the #define directive in C?
   • A) To define a constant
   • B) To define a function
   • C) To include a header file
   • D) To conditionally compile code
2. Which of the following is the correct syntax for defining a macro?
   • A) #define MAX 100
   • B) define MAX = 100
   • C) #macro MAX 100
   • D) macro #define MAX 100
3. In C, what does the #define directive do at compile-time?
   • A) Defines a new variable
   • B) Replaces code with the defined macro
   • C) Includes a library
   • D) Initializes memory
4. Which of the following is true about #define?
   • A) It creates a constant value that can be modified
   • B) It substitutes the value at compile time
   • C) It is only used for functions
   • D) It can be used for dynamic memory allocation
5. What will happen if you define a macro with the same name multiple times?
   • A) Compilation will fail
   • B) The last definition is taken into account
   • C) The first definition is used
   • D) It will throw a runtime error

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Conditional Compilation (#ifdef, #ifndef, #endif)

6. What does the #ifdef preprocessor directive check for?
   • A) If the macro is not defined
   • B) If a macro is defined
   • C) If a function is defined
   • D) If a header file exists
7. What is the purpose of #ifndef in conditional compilation?
   • A) To check if a macro is defined
   • B) To check if a macro is not defined
   • C) To ignore a file
   • D) To include a file
8. Which of the following is a valid use of the #endif directive?
   • A) To end a conditional compilation block
   • B) To define a macro
   • C) To include a header file
   • D) To terminate a function
9. Which directive is used to define code that should be conditionally compiled if a macro is not defined?
   • A) #if
   • B) #ifdef
   • C) #ifndef
   • D) #else
10. If a macro is not defined, the following code block will be compiled:cCopy code#ifndef MY_MACRO // code block #endif
    • A) True
    • B) False

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File Inclusion (#include)

11. What is the purpose of the #include directive in C?

• A) To define a macro
• B) To include the contents of a file
• C) To compile a file
• D) To create a function

12. Which of the following will include a standard library in C?

• A) #include <stdio.h>
• B) #include "myfile.h"
• C) #include stdlib
• D) #include library.h

13. When using #include, what is the difference between #include <file.h> and #include "file.h"?

• A) The first searches for the file in system directories; the second searches in the current directory
• B) The first searches for the file in the current directory; the second searches in system directories
• C) Both are the same
• D) Both include the file at runtime

14. Which of the following is the correct syntax to include a user-defined header file?

• A) #include <userfile.h>
• B) #include "userfile.h"
• C) #include {userfile.h}
• D) #include [userfile.h]

15. What happens if a file is included multiple times?

• A) It will result in a compilation error
• B) The compiler will ignore subsequent inclusions
• C) It will cause a runtime error
• D) It will be included multiple times

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Macro Functions

16. What is a macro function in C?

• A) A function defined with the #define directive
• B) A function with a fixed value
• C) A regular function with a return type
• D) A function declared inside a header file

17. Which of the following is the correct syntax for defining a macro function?

• A) #define square(x) x*x
• B) #define square(x) (x*x)
• C) macro square(x) x*x
• D) function square(x) x*x

18. In macro functions, why is it important to use parentheses around parameters?

• A) To ensure proper evaluation of expressions
• B) To avoid compile-time errors
• C) To handle multiple arguments
• D) To increase performance

19. What is the potential drawback of using macro functions instead of regular functions?

• A) They cannot be debugged
• B) They may lead to unintended side effects
• C) They are slower than regular functions
• D) They cannot take parameters

20. Which of the following is true about a macro function?

• A) It operates at runtime
• B) It works as a preprocessor directive
• C) It always returns a value
• D) It can be dynamically allocated

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Predefined Macros and Operators (#, ##)

21. What does the # operator do in a macro definition?

• A) Concatenates two tokens
• B) Converts a macro argument into a string
• C) Adds two values
• D) Defines a constant

22. What does the ## operator do in a macro definition?

• A) Replaces all arguments with values
• B) Concatenates two tokens into one
• C) Converts a value into a string
• D) Checks if a macro is defined

23. Which predefined macro can be used to get the current line number in C?

• A) __LINE__
• B) __DATE__
• C) __TIME__
• D) __FILE__

24. Which predefined macro returns the current date in C?

• A) __DATE__
• B) __TIME__
• C) __LINE__
• D) __FILE__

25. Which predefined macro is used to get the current file name in C?

• A) __FILE__
• B) __DATE__
• C) __LINE__
• D) __TIME__

26. What does the following code do?cCopy code#define CONCAT(x, y) x ## y

• A) Concatenates two strings
• B) Concatenates two variables or tokens
• C) Defines a function
• D) Adds two numbers

27. What is the result of the following code?cCopy code#define PRINT(x) printf(#x) PRINT(Hello);

• A) It will print “Hello”
• B) It will print Hello
• C) It will cause a syntax error
• D) It will cause a compilation error

28. Which of the following is a valid use of the # operator?

• A) #define MAX (5)
• B) #define SQUARE(x) x #x
• C) #define stringify(x) #x
• D) #define CONCAT(x, y) x ## y

29. How would you use the ## operator to join two variables num and 1 into num1?

• A) #define JOIN(num, 1) num ## 1
• B) #define JOIN(num, 1) num1
• C) #define JOIN(num, 1) num & 1
• D) #define JOIN(num, 1) num ## 1

30. Which predefined macro returns the current time of compilation?

• A) __TIME__
• B) __DATE__
• C) __LINE__
• D) __FILE__

Answers (Tabular Form)

Question	Answer
1	A
2	A
3	B
4	B
5	B
6	B
7	B
8	A
9	C
10	A
11	B
12	A
13	A
14	B
15	B
16	A
17	B
18	A
19	B
20	B
21	B
22	B
23	A
24	A
25	A
26	B
27	A
28	C
29	A
30	A