Nested structures - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested struct member access

What is the output of this C code snippet?

C

typedef struct {
    int x;
    int y;
} Point;

typedef struct {
    Point topLeft;
    Point bottomRight;
} Rectangle;

#include <stdio.h>

int main() {
    Rectangle rect = {{1, 2}, {3, 4}};
    printf("%d\n", rect.bottomRight.x);
    return 0;
}

A 2

B 4

C 3

D 1

💡 Hint

Look at how the nested structs are initialized and accessed.

The Rectangle struct has two Point members: topLeft and bottomRight. The code prints rect.bottomRight.x, which is initialized to 3.

❓ Predict Output

intermediate

Value of nested struct after assignment

What is the value of p2.y after this code runs?

C

typedef struct {
    int x;
    int y;
} Point;

#include <stdio.h>

int main() {
    Point p1 = {5, 10};
    Point p2;
    p2 = p1;
    p2.y = 20;
    printf("%d\n", p2.y);
    return 0;
}

A 20

B 5

C 10

D 0

💡 Hint

Remember that assigning structs copies all members.

p2 is assigned p1, then p2.y is changed to 20, so printing p2.y outputs 20.

❓ Predict Output

advanced

Output of nested struct pointer access

What does this program print?

C

typedef struct {
    int id;
    struct {
        int day;
        int month;
        int year;
    } date;
} Event;

#include <stdio.h>

int main() {
    Event e = {101, {15, 8, 2023}};
    Event *ptr = &e;
    printf("%d-%d-%d\n", ptr->date.day, ptr->date.month, ptr->date.year);
    return 0;
}

A 101-15-8

B 15-8-2023

C 8-15-2023

D 2023-8-15

💡 Hint

Use the arrow operator to access nested struct members through a pointer.

The pointer ptr points to e. Accessing ptr->date.day etc. prints the date in day-month-year order.

❓ Predict Output

advanced

Result of modifying nested struct via pointer

What is the output of this program?

C

typedef struct {
    int x;
    int y;
} Point;

typedef struct {
    Point center;
    int radius;
} Circle;

#include <stdio.h>

int main() {
    Circle c = {{0, 0}, 5};
    Circle *pc = &c;
    pc->center.x = 10;
    printf("%d\n", c.center.x);
    return 0;
}

A 10

B 0

C Compilation error

D 5

💡 Hint

Changing a nested struct member via pointer affects the original struct.

The pointer pc points to c. Changing pc->center.x changes c.center.x to 10.

❓ Predict Output

expert

Output of complex nested struct initialization and access

What is the output of this program?

C

typedef struct {
    int day;
    int month;
    int year;
} Date;

typedef struct {
    char name[20];
    Date birthdate;
} Person;

#include <stdio.h>

int main() {
    Person people[2] = {
        {"Alice", {1, 1, 2000}},
        {"Bob", {31, 12, 1999}}
    };
    printf("%s was born on %d/%d/%d\n", people[1].name, people[1].birthdate.day, people[1].birthdate.month, people[1].birthdate.year);
    return 0;
}

A Alice was born on 31/12/1999

B Alice was born on 1/1/2000

C Bob was born on 1/1/2000

D Bob was born on 31/12/1999

💡 Hint

Check the array index and nested struct initialization carefully.

people[1] refers to the second element, Bob, with birthdate 31/12/1999.

Practice

1. What is a nested structure in C programming?

easy

A. A structure that contains another structure as a member

B. A structure with only one member

C. A structure declared inside a function

D. A structure that uses pointers only

Solution

1. Step 1: Understand structure composition

   A nested structure means one structure is included inside another as a member.

2. Step 2: Rule out distractors

   The other options describe unrelated concepts: a structure using pointers only, with only one member, or declared inside a function.

3. Final Answer:

   A structure that contains another structure as a member -> Option A

4. Quick Check:

   Nested structure = structure inside structure [OK]

Hint: Nested means one structure inside another [OK]

Common Mistakes:

• Thinking nested means pointer usage
• Confusing nested with single-member structures
• Assuming nested means declared inside functions

2. Which of the following is the correct syntax to access a member of a nested structure in C?

easy

A. outer.inner->member

B. outer->inner->member

C. outer.inner.member

D. outer->inner.member

Solution

1. Step 1: Identify access operator for nested structures

   When using nested structures (not pointers), use dot notation for each level: outer.inner.member.

2. Step 2: Understand pointer vs non-pointer access

   Arrow (->) is used only when accessing members through pointers, which is not stated here.

3. Final Answer:

   outer.inner.member -> Option C

4. Quick Check:

   Use dot for nested struct members [OK]

Hint: Use dot notation for nested struct members [OK]

Common Mistakes:

• Using arrow (->) when not using pointers
• Mixing dot and arrow incorrectly
• Confusing member access syntax

3. What is the output of the following C code?

typedef struct {
    int day;
    int month;
    int year;
} Date;

typedef struct {
    char name[20];
    Date birthday;
} Person;

int main() {
    Person p = {"Alice", {15, 8, 1990}};
    printf("%d-%d-%d", p.birthday.day, p.birthday.month, p.birthday.year);
    return 0;
}

medium

A. 15-8-1990

B. Alice-15-8

C. 1990-8-15

D. Compilation error

Solution

1. Step 1: Understand structure initialization

   Person p is initialized with name "Alice" and birthday as Date {15, 8, 1990}.

2. Step 2: Trace printf output

   printf prints p.birthday.day (15), p.birthday.month (8), p.birthday.year (1990) separated by dashes.

3. Final Answer:

   15-8-1990 -> Option A

4. Quick Check:

   Print nested struct members correctly [OK]

Hint: Access nested members with dot notation [OK]

Common Mistakes:

• Printing name instead of date
• Mixing order of day, month, year
• Forgetting to initialize nested struct

4. Identify the error in this nested structure code snippet:

struct Address {
    char city[20];
    int zip;
};

struct Employee {
    char name[30];
    struct Address addr;
};

int main() {
    struct Employee emp;
    emp.addr->zip = 12345;
    return 0;
}

medium

A. Missing semicolon after struct definitions

B. Using '->' operator on a non-pointer structure variable

C. Incorrect declaration of nested structure

D. Cannot assign integer to zip member

Solution

1. Step 1: Check member access syntax

   emp.addr is a structure variable, not a pointer, so '->' operator is invalid here.

2. Step 2: Correct operator usage

   Use dot operator '.' to access zip: emp.addr.zip = 12345;

3. Final Answer:

   Using '->' operator on a non-pointer structure variable -> Option B

4. Quick Check:

   Use '.' for struct variables, '->' for pointers [OK]

Hint: Use '.' for struct, '->' only for pointers [OK]

Common Mistakes:

• Using '->' on struct variables
• Confusing pointer and non-pointer access
• Ignoring compiler error messages

5. Given the following nested structures, how would you write a function in C that takes a Person and returns the birth year?

typedef struct {
    int day;
    int month;
    int year;
} Date;

typedef struct {
    char name[50];
    Date birthday;
} Person;

// Function prototype here

Which of the following is the correct function definition?

hard

A. int getBirthYear(Person *p) { return p.birthday->year; }

B. int getBirthYear(Person *p) { return p->birthday.year; }

C. int getBirthYear(Person p) { return p.year; }

D. int getBirthYear(Person p) { return p.birthday.year; }

Solution

1. Step 1: Understand parameter passing

   The function takes a Person by value, so use dot notation to access members.

2. Step 2: Access nested member correctly

   Access birthday.year as p.birthday.year since p is not a pointer.

3. Final Answer:

   int getBirthYear(Person p) { return p.birthday.year; } -> Option D

4. Quick Check:

   Use dot for struct value parameters [OK]

Hint: Use dot for struct, arrow for pointer parameters [OK]

Common Mistakes:

• Using arrow (->) on non-pointer parameter
• Accessing wrong member name
• Confusing pointer and value parameter syntax