What is the output of: #define ADD(x,y) (x+y) int main() { printf("%d", ADD(5,3)*2); return 0; }

The correct answer is A: 16. ADD(5,3)*2 expands to (5+3)*2 = 8*2 = 16. Parentheses around the entire macro definition protect against precedence issues.

struct Node { int data; struct Node *next; }; This is an example of which design pattern?

The correct answer is B: Self-referential structure. A self-referential structure contains a pointer to its own type. This is the fundamental building block for creating linked lists, trees, and other dynamic data structures.

Which keyword is used to declare a variable that maintains its value between function calls?

The correct answer is B: static. The 'static' keyword gives a variable static storage duration, preserving its value between function calls.

Which variable declaration is correct in C?

The correct answer is C: char _var123;. Variable names must start with a letter or underscore, followed by letters, digits, or underscores. Option C follows this rule correctly.

What is the correct way to allocate and initialize a structure dynamically? struct Node { int data; int next; };

The correct answer is D: Both A and B are equally correct. Both A and B allocate memory correctly; B includes explicit typecasting which is optional in C but good practice.

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C Programming
Structures & Unions

C language from basics to advanced placement prep

46 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 46

Topics in C Programming

All Basics & Syntax 86 Data Types & Variables 97 Control Flow 100 Functions 99 Arrays & Strings 100 Pointers 99 Structures & Unions 100 File Handling 100 Dynamic Memory 98 Preprocessor 99

Q.31 Medium Structures & Unions

Which initialization method for structures is used in designated initializers (C99 feature)?

A struct s obj = {1, 2, 3};

B struct s obj = {.x = 1, .y = 2};

C struct s obj[]; obj[0].x = 1;

D struct s *obj = malloc(...);

Correct Answer: B. struct s obj = {.x = 1, .y = 2};

EXPLANATION

Designated initializers (C99) allow specifying members by name using dot notation, making code more readable and maintainable.

Test

Q.32 Medium Structures & Unions

What will be the behavior of this code? struct s { int a; }; struct s obj = {5}; struct s *ptr = &obj; ptr->a = 10; printf("%d", obj.a);

A 5

B 10

C Garbage value

D Compilation error

Correct Answer: B. 10

EXPLANATION

ptr points to obj, so ptr->a = 10 modifies obj.a to 10. The printf outputs the modified value 10.

Test

Q.33 Medium Structures & Unions

What is the difference between struct tag and struct type in C?

A Tag is the variable name, type is the structure name

B Tag is the structure name, type is the variable declaration

C They are the same thing

D Type is used in unions only

Correct Answer: B. Tag is the structure name, type is the variable declaration

EXPLANATION

In 'struct person { int age; } p;', 'person' is the tag (structure name) and 'p' is the type/variable. Tag names the structure template; type creates actual instances.

Test

Q.34 Medium Structures & Unions

Which statement is correct about bit fields in structures?

A They can be applied to any data type

B They are used to pack multiple members into fewer bytes

C They increase the structure size

D They make structures faster to access

Correct Answer: B. They are used to pack multiple members into fewer bytes

EXPLANATION

Bit fields allow you to specify the number of bits for integral members, enabling memory optimization by packing multiple small values into a single byte.

Test

Q.35 Medium Structures & Unions

What happens when you modify a union member that overlaps with another?

A Both members update independently

B The previous member value is preserved

C The previous member's value gets overwritten

D A compilation error occurs

Correct Answer: C. The previous member's value gets overwritten

EXPLANATION

Since union members share memory, modifying one member overwrites the value of other members because they occupy the same memory location.

Test

Q.36 Medium Structures & Unions

Which of the following correctly initializes a structure array? struct point { int x, y; } arr[3] = ?

A { {1,2}, {3,4}, {5,6} }

B { 1,2,3,4,5,6 }

C [ {1,2}, {3,4}, {5,6} ]

D None of the above

Correct Answer: A. { {1,2}, {3,4}, {5,6} }

EXPLANATION

Structure arrays are initialized with nested braces, where each set of braces contains initialization values for one structure element.

Test

Q.37 Medium Structures & Unions

In a nested structure, how do you access the innermost member? struct outer { struct inner { int value; } in; } obj;

A obj.value

B obj.in.value

C obj->in->value

D obj.in->value

Correct Answer: B. obj.in.value

EXPLANATION

For nested structures accessed through an object, use the dot operator multiple times: obj.in.value accesses the value member of the inner structure.

Test

Q.38 Medium Structures & Unions

What will be printed by this code? struct s { int a; struct s *next; }; struct s *ptr; sizeof(struct s)

A 4 bytes

B 8 bytes

C 12 bytes

D 16 bytes

Correct Answer: C. 12 bytes

EXPLANATION

sizeof(int) = 4 bytes, sizeof(pointer) = 8 bytes (on 64-bit systems). Total = 12 bytes. Pointers are fixed size regardless of what they point to.

Test

Q.39 Medium Structures & Unions

Consider struct test { int x; double y; char z; }; What is the minimum size of this structure (assuming 4-byte int, 8-byte double)?

A 13 bytes

B 16 bytes

C 20 bytes

D 24 bytes

Correct Answer: D. 24 bytes

EXPLANATION

Due to padding: int (4) + padding (4) + double (8) + char (1) + padding (3) = 24 bytes. The structure aligns to the largest member size.

Test

Q.40 Medium Structures & Unions

Consider: union u { int x; double y; }; What is sizeof(u)?

A 4 bytes

B 8 bytes

C 12 bytes

D 16 bytes

Correct Answer: B. 8 bytes

EXPLANATION

The size of a union is equal to its largest member. double is typically 8 bytes, which is larger than int (4 bytes).

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