Defining structures - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of structure member assignment

What is the output of this C program?

C

#include <stdio.h>

struct Point {
    int x;
    int y;
};

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

A Compilation error

B 10 5

C 5 10

D 0 0

💡 Hint

Remember how structure members are assigned and accessed.

The structure 'Point' has two integer members x and y. We assign 5 to x and 10 to y, then print them in order. So output is '5 10'.

❓ Predict Output

intermediate

Size of structure with padding

What is the output of this program printing the size of the structure?

C

#include <stdio.h>

struct Data {
    char a;
    int b;
};

int main() {
    printf("%zu\n", sizeof(struct Data));
    return 0;
}

A 4

B 5

C 6

D 8

💡 Hint

Think about how the compiler aligns data in memory.

The structure has a char (1 byte) and an int (usually 4 bytes). Due to padding for alignment, the total size is 8 bytes, not 5.

🔧 Debug

advanced

Identify the error in structure initialization

What error will this code produce when compiled?

C

#include <stdio.h>

struct Person {
    char name[10];
    int age;
};

int main() {
    struct Person p = {"Alice", 30, 100};
    printf("%s %d\n", p.name, p.age);
    return 0;
}

A Compilation error: too many initializers

B Runs and prints: Alice 30

C Runtime error: segmentation fault

D Compilation error: missing semicolon

💡 Hint

Check how many values are given for initialization compared to members.

The structure has two members but three values are given in initialization. This causes a compilation error for too many initializers.

❓ Predict Output

advanced

Output of nested structures

What is the output of this program?

C

#include <stdio.h>

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

struct Event {
    char name[20];
    struct Date date;
};

int main() {
    struct Event e = {"Meeting", {15, 8, 2024}};
    printf("%s on %d/%d/%d\n", e.name, e.date.day, e.date.month, e.date.year);
    return 0;
}

A Meeting on 8/15/2024

B Meeting on 15/8/2024

C Compilation error

D Meeting on 0/0/0

💡 Hint

Look at how nested structures are initialized and accessed.

The nested structure Date is initialized with day=15, month=8, year=2024. The print statement outputs these values in order.

🧠 Conceptual

expert

Number of items in an array of structures

Given this code, how many elements does the array 'books' contain?

C

struct Book {
    char title[50];
    int pages;
};

struct Book books[] = {
    {"Book A", 100},
    {"Book B", 150},
    {"Book C", 200}
};

A 3

B 2

C 0

D 50

💡 Hint

Count the number of initializers in the array.

The array 'books' is initialized with three elements, so it contains 3 items.

Practice

1. What is the purpose of using struct in C programming?

easy

A. To allocate memory dynamically

B. To create a loop structure

C. To group different data types under one name

D. To define a function

Solution

1. Step 1: Understand the role of struct

   The struct keyword is used to group variables of different types into a single unit.

2. Step 2: Compare with other options

   Options A, B, and C relate to memory allocation, loops, and functions, which are unrelated to struct.

3. Final Answer:

   To group different data types under one name -> Option C

4. Quick Check:

   struct groups data types = D [OK]

Hint: Remember: struct bundles variables like a box [OK]

Common Mistakes:

• Confusing struct with loops or functions
• Thinking struct allocates memory dynamically
• Assuming struct defines a single data type only

2. Which of the following is the correct syntax to define a structure named Person with members int age and char name[20]?

easy

A. struct Person { int age; char name[20]; };

B. struct Person ( int age; char name[20]; );

C. struct Person = { int age; char name[20]; };

D. struct Person: int age; char name[20];

Solution

1. Step 1: Recall correct struct syntax

   Structures are defined using curly braces { } with semicolons after each member.

2. Step 2: Check each option

   struct Person { int age; char name[20]; }; uses correct braces and semicolons. Options B, C, and D use incorrect symbols or missing braces.

3. Final Answer:

   struct Person { int age; char name[20]; }; -> Option A

4. Quick Check:

   Correct struct syntax uses braces and semicolons = A [OK]

Hint: Use braces { } and semicolons ; inside struct [OK]

Common Mistakes:

• Using parentheses instead of braces
• Missing semicolons after members
• Using equal sign or colon incorrectly

3. What will be the output of the following code?

struct Point { int x; int y; } p = {3, 4};
printf("%d %d", p.x, p.y);

medium

A. 0 0

B. 3 4

C. 4 3

D. Compilation error

Solution

1. Step 1: Understand struct initialization

   The struct Point is initialized with p = {3, 4}, so p.x = 3 and p.y = 4.

2. Step 2: Analyze printf output

   The printf prints p.x and p.y in order, so output is "3 4".

3. Final Answer:

   3 4 -> Option B

4. Quick Check:

   p.x=3 and p.y=4 prints as "3 4" [OK]

Hint: Struct members print in order of initialization [OK]

Common Mistakes:

• Mixing order of members in output
• Assuming default zero values
• Thinking code causes compilation error

4. Identify the error in the following code snippet:

struct Car {
  int speed;
  char model[10];
};

struct Car c;
c.speed = 100;
c.model = "Sedan";

medium

A. Cannot assign string directly to array member

B. Missing semicolon after struct definition

C. Incorrect struct keyword usage

D. Variable c not declared

Solution

1. Step 1: Check struct definition and declaration

   The struct is correctly defined and variable c declared.

2. Step 2: Analyze assignment to c.model

   Arrays cannot be assigned directly with = operator; string copy functions like strcpy are needed.

3. Final Answer:

   Cannot assign string directly to array member -> Option A

4. Quick Check:

   Array assignment needs strcpy, not = [OK]

Hint: Use strcpy to assign strings to char arrays [OK]

Common Mistakes:

• Assigning string literals directly to char arrays
• Forgetting to include string.h for strcpy
• Assuming semicolon or declaration errors

5. Given the structure definition:

struct Employee {
  int id;
  char name[30];
  float salary;
};

Which of the following code snippets correctly creates an Employee variable and initializes all members in one statement?

hard

A. struct Employee e; e.id = 101; e.name = "Alice"; e.salary = 75000.0;

B. struct Employee e = {id:101, name:"Alice", salary:75000.0};

C. struct Employee e = (101, "Alice", 75000.0);

D. struct Employee e = {101, "Alice", 75000.0};

Solution

1. Step 1: Check initialization syntax for struct

   Structs can be initialized with braces { } listing values in order of members.

2. Step 2: Evaluate each option

   struct Employee e = {101, "Alice", 75000.0}; uses correct brace initialization. struct Employee e; e.id = 101; e.name = "Alice"; e.salary = 75000.0; tries to assign string directly to array (invalid). struct Employee e = (101, "Alice", 75000.0); uses parentheses incorrectly. struct Employee e = {id:101, name:"Alice", salary:75000.0}; uses named initialization which is not standard in C.

3. Final Answer:

   struct Employee e = {101, "Alice", 75000.0}; -> Option D

4. Quick Check:

   Brace list initialization is correct for structs [OK]

Hint: Use braces with values in order to initialize structs [OK]

Common Mistakes:

• Assigning strings directly to arrays after declaration
• Using parentheses instead of braces
• Trying named member initialization (not standard C)