C Programming — Structures & Unions Questions & Answers

Q.1 Medium Structures & Unions

Which of the following statements about structure initialization in C is INCORRECT?

A Designated initializers allow setting members in any order

B All members must be explicitly initialized during declaration

C Members can be initialized during structure definition

D Partial initialization results in uninitialized members having indeterminate values

Correct Answer: B. All members must be explicitly initialized during declaration

EXPLANATION

Members do not need to be explicitly initialized. Uninitialized members in automatic structures have indeterminate values, while static structures have zero-initialized members. Designated initializers (C99+) allow flexible initialization order.

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Q.2 Medium Structures & Unions

In the context of bit fields in structures, what is the maximum number of bits that can be allocated to a single member in standard C?

A 8 bits

B 16 bits

C Size of the underlying type in bits

D 32 bits

Correct Answer: C. Size of the underlying type in bits

EXPLANATION

The maximum number of bits for a bit field member cannot exceed the size of the underlying type. For int (typically 32 bits), you can allocate up to 32 bits to a single member.

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Q.3 Medium Structures & Unions

Which feature in C allows you to define a structure without a tag name for use within another structure?

A Tagged union

B Anonymous structure

C Typedef structure

D Nested enumeration

Correct Answer: B. Anonymous structure

EXPLANATION

Anonymous structures allow defining structures without a tag name directly inside another structure, making members accessible as if they belong to the outer structure.

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Q.4 Medium Structures & Unions

Consider the following code:
struct Data {
int x;
char y;
double z;
};
Assuming int=4 bytes, char=1 byte, double=8 bytes, what is the size of struct Data due to padding?

A 13 bytes

B 16 bytes

C 20 bytes

D 24 bytes

Correct Answer: D. 24 bytes

EXPLANATION

Memory alignment causes padding. x(4) + padding(4) + y(1) + padding(7) + z(8) = 24 bytes. The compiler aligns to the largest member (double = 8 bytes).

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Q.5 Medium Structures & Unions

Consider this structure: struct Complex { int real; int imag; }; If you want to create an array of 100 such structures, which declaration is correct?

A struct Complex c[100];

B struct Complex *c = (struct Complex *)malloc(100);

C struct Complex c = {100};

D struct Complex c[100][100];

Correct Answer: A. struct Complex c[100];

EXPLANATION

Option A correctly creates a static array of 100 structures. Option B creates a pointer (and allocates incorrect size).

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Q.6 Medium Structures & Unions

What is the purpose of using anonymous structures/unions?

A To reduce memory usage

B To access members without using the intermediate struct name

C To improve execution speed

D To hide members from external access

Correct Answer: B. To access members without using the intermediate struct name

EXPLANATION

Anonymous structures allow direct member access without needing to reference the nested structure name.

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Q.7 Medium Structures & Unions

In a nested structure scenario like struct A contains struct B, how do you access a member of B from A's variable?

A a_var->b_member

B a_var.b_var.c_member

C Both A and B are correct depending on context

D a_var..c_member

Correct Answer: C. Both A and B are correct depending on context

EXPLANATION

If B is embedded in A: a_var.b_var.member. If B is a pointer in A: a_var->b_var->member or a_var.b_ptr->member.

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Q.8 Medium Structures & Unions

Which of the following is a valid way to pass a structure to a function?

A Pass by value only

B Pass by pointer only

C Both pass by value and pass by pointer

D Pass by reference only

Correct Answer: C. Both pass by value and pass by pointer

EXPLANATION

Structures can be passed by value (copying the entire structure) or by pointer (passing address) for efficiency.

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Q.9 Medium Structures & Unions

What will happen if you try to compare two structures using the == operator directly?

A It compares all members automatically

B It results in a compilation error

C It returns the comparison of the first members only

D It compares the memory addresses of the structures

Correct Answer: B. It results in a compilation error

EXPLANATION

C does not support direct comparison of structures using ==. You must compare members individually or use memcmp().

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Q.10 Medium Structures & Unions

Consider a structure with bit fields:
struct Flags {
unsigned int flag1 : 1;
unsigned int flag2 : 3;
unsigned int flag3 : 4;
};
What is the minimum size of this structure?

A 1 byte

B 2 bytes

C 4 bytes

D 8 bytes

Correct Answer: C. 4 bytes

EXPLANATION

Bit fields must fit within an underlying integer type. Total bits = 8, which requires at least 4 bytes (one int on most systems).

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