Array of structures - Mini Project: Build & Apply

Array of structures

📖 Scenario: You are managing a small library system. You want to store information about books including their title and number of pages.

🎯 Goal: Create an array of structures to hold book information, then print the details of each book.

📋 What You'll Learn

Define a structure named Book with two members: title (string) and pages (integer).

Create an array named library of 3 Book structures with exact titles and page counts.

Use a loop to print each book's title and page count.

💡 Why This Matters

🌍 Real World

Storing and managing collections of related data like books, students, or products is common in software applications.

💼 Career

Understanding arrays of structures is essential for working with complex data in C programming jobs, especially in systems programming and embedded development.

1

Define the Book structure and create the library array

Define a structure called Book with a char array title[50] and an int pages. Then create an array called library of 3 Book elements with these exact entries: {"C Programming", 250}, {"Data Structures", 300}, {"Algorithms", 400}.

C

// Define the Book structure and create the library array
// Your code here

Hint

Use struct keyword to define the structure. Use curly braces to initialize the array with exact titles and pages.

2

Create a variable to hold the number of books

Create an int variable called num_books and set it to 3 to represent the number of books in the library array.

C

#include 

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

struct Book library[3] = {
    {"C Programming", 250},
    {"Data Structures", 300},
    {"Algorithms", 400}
};

// Create an int variable num_books and set it to 3
// Your code here

Hint

Just create a simple integer variable and assign the value 3.

3

Use a for loop to print each book's details

Write a for loop using int i from 0 to less than num_books. Inside the loop, print the book's title and pages using library[i].title and library[i].pages.

C

#include 

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

struct Book library[3] = {
    {"C Programming", 250},
    {"Data Structures", 300},
    {"Algorithms", 400}
};

int num_books = 3;

// Use a for loop to print each book's title and pages
// Your code here

Hint

Use a for loop with i from 0 to num_books - 1. Use printf to show the title and pages.

4

Print the final output

Run the program to print the details of all books in the library array.

C

#include 

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

struct Book library[3] = {
    {"C Programming", 250},
    {"Data Structures", 300},
    {"Algorithms", 400}
};

int num_books = 3;

int main() {
    for (int i = 0; i < num_books; i++) {
        printf("Title: %s, Pages: %d\n", library[i].title, library[i].pages);
    }
    return 0;
}

// Run the program to see the output

Hint

Make sure your program prints each book's title and pages on a new line exactly as shown.

Practice

1. What is the correct way to declare an array of 5 structures named Student in C?

easy

A. Student arr[5];

B. struct Student arr;

C. Student arr;

D. struct arr[5];

Solution

1. Step 1: Understand structure array declaration

   To declare an array of structures, use the structure type followed by the array name and size in square brackets.

2. Step 2: Apply correct syntax for array of structures

   Since Student is the structure type, Student arr[5]; declares an array of 5 Student structures.

3. Final Answer:

   Student arr[5]; -> Option A

4. Quick Check:

   Array of structures = type name[size] [OK]

Hint: Use type name[size] to declare structure arrays [OK]

Common Mistakes:

• Forgetting 'struct' keyword if not typedefed
• Declaring single structure instead of array
• Using wrong syntax like struct arr[5];

2. Which of the following is the correct syntax to access the age member of the 3rd element in an array students of structures?

easy

A. students->age[3];

B. students.age[3];

C. students[3].age;

D. students[2].age;

Solution

1. Step 1: Understand zero-based indexing in arrays

   Arrays in C start at index 0, so the 3rd element is at index 2.

2. Step 2: Access structure member using dot operator

   Use students[2].age to access the age member of the 3rd element.

3. Final Answer:

   students[2].age; -> Option D

4. Quick Check:

   3rd element = index 2, use dot for member [OK]

Hint: Remember arrays start at 0; 3rd element is index 2 [OK]

Common Mistakes:

• Using index 3 instead of 2 for 3rd element
• Using arrow operator on array elements
• Accessing member as students.age[3]

3. Consider the code:

typedef struct {
  int id;
  char name[10];
} Item;

Item items[2] = {{1, "Pen"}, {2, "Book"}};

printf("%s", items[1].name);

What will be the output?

medium

A. Pen

B. Book

C. items[1].name

D. Compilation error

Solution

1. Step 1: Identify the array initialization

   The array items has two elements: first with id=1, name="Pen"; second with id=2, name="Book".

2. Step 2: Understand printf access

   items[1].name accesses the second element's name, which is "Book".

3. Final Answer:

   Book -> Option B

4. Quick Check:

   items[1].name = "Book" [OK]

Hint: Index 1 accesses second element's name [OK]

Common Mistakes:

• Confusing index 0 and 1
• Expecting id to print instead of name
• Syntax errors in initialization

4. What is wrong with this code snippet?

struct Point {
  int x, y;
};

struct Point points[3];
points[0].x = 10;
points[0].y = 20;
points[1].x = 30;
points[1].y = 40;
points[2].x = 50;
points[2].y = 60;

printf("%d", points[3].x);

medium

A. Array size should be 4 instead of 3

B. Missing semicolon after struct definition

C. Accessing points[3] is out of bounds

D. Incorrect struct member access syntax

Solution

1. Step 1: Check array size and indexing

   The array points has size 3, valid indices are 0, 1, 2.

2. Step 2: Identify invalid access

   Accessing points[3] is out of bounds and causes undefined behavior.

3. Final Answer:

   Accessing points[3] is out of bounds -> Option C

4. Quick Check:

   Array index must be less than size [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Using index equal to array size
• Ignoring array bounds errors
• Assuming array auto-expands

5. You have a structure Employee with members int id; and float salary;. How do you write a function in C that takes an array of Employee and its size, then returns the average salary?

hard

A. float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i

B. float averageSalary(Employee *emp, int n) { float sum=0; for(int i=0;isalary; return sum/n; }

C. float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i

D. float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i

Solution

1. Step 1: Loop through array elements correctly

   Use a for loop from 0 to n-1 and access each element with emp[i].

2. Step 2: Sum the salary member of each element

   Access salary as emp[i].salary and add to sum, then divide by n.

3. Final Answer:

   float averageSalary(Employee emp[], int n) { float sum=0; for(int i=0;i -> Option A

4. Quick Check:

   Loop + emp[i].salary sum / n = average [OK]

Hint: Use emp[i].member to access array struct members [OK]

Common Mistakes:

• Using emp->salary inside loop instead of emp[i].salary
• Accessing emp.salary instead of emp[i].salary
• Adding whole struct instead of member