Accessing structure members - Mini Project: Build & Apply

Accessing structure members

📖 Scenario: You are working on a simple program to store and display information about a book. You will create a structure to hold the book's title and number of pages, then access and print these details.

🎯 Goal: Build a C program that defines a struct for a book with a title and page count, assigns values to its members, and prints them.

📋 What You'll Learn

Define a struct named Book with members title (string) and pages (integer).

Create a variable of type Book named myBook.

Assign the title "C Programming" to myBook.title.

Assign the number 250 to myBook.pages.

Print the book's title and page count using printf.

💡 Why This Matters

🌍 Real World

Structures help organize related data together, like storing information about books, students, or products in a program.

💼 Career

Understanding structures is essential for C programming jobs, especially in systems programming, embedded systems, and software development where grouping data logically is important.

1

Define the Book structure

Define a struct named Book with two members: title as a character array of size 50, and pages as an integer.

C

# Define the struct Book with members title and pages
// Your code here

Hint

Use struct Book { char title[50]; int pages; }; to define the structure.

2

Create a Book variable and assign values

Create a variable named myBook of type struct Book. Assign the string "C Programming" to myBook.title using strcpy, and assign the integer 250 to myBook.pages. Include #include <string.h> at the top.

C

#include 
#include 

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

// Create myBook and assign values
// Your code here

Hint

Remember to include #include <string.h> to use strcpy.

3

Access and print the structure members

Inside the main function, use printf to print the book's title and page count from myBook. Use myBook.title and myBook.pages to access the members.

C

#include 
#include 

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

int main() {
    struct Book myBook;
    strcpy(myBook.title, "C Programming");
    myBook.pages = 250;
    // Print the book title and pages
    // Your code here
    return 0;
}

Hint

Use printf("Title: %s\n", myBook.title); and printf("Pages: %d\n", myBook.pages); to print.

4

Run and check the output

Run the program and ensure it prints exactly:
Title: C Programming
Pages: 250

C

#include 
#include 

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

int main() {
    struct Book myBook;
    strcpy(myBook.title, "C Programming");
    myBook.pages = 250;
    printf("Title: %s\n", myBook.title);
    printf("Pages: %d\n", myBook.pages);
    // Check output
}

Hint

Make sure your output matches exactly, including capitalization and spacing.

Practice

1. Which operator is used to access members of a structure variable in C?

easy

A. Colon operator (:)

B. Arrow operator (->)

C. Double colon (::)

D. Dot operator (.)

Solution

1. Step 1: Understand structure member access

   In C, when you have a structure variable, you use the dot operator (.) to access its members.

2. Step 2: Differentiate from pointer access

   The arrow operator (->) is used when you have a pointer to a structure, not the structure variable itself.

3. Final Answer:

   Dot operator (.) -> Option D

4. Quick Check:

   Structure variable member access = dot operator (.) [OK]

Hint: Use dot (.) for struct variables, arrow (->) for pointers [OK]

Common Mistakes:

• Confusing dot (.) with arrow (->) operator
• Using colon (:) which is invalid in C
• Using double colon (::) which is from other languages

2. Given the structure struct Point { int x; int y; } p;, which is the correct way to assign 10 to member x?

easy

A. p->x = 10;

B. p:x = 10;

C. p.x = 10;

D. p[x] = 10;

Solution

1. Step 1: Identify the variable type

   Here, p is a structure variable, not a pointer.

2. Step 2: Use correct member access syntax

   For structure variables, use the dot operator (.) to access members, so p.x = 10; is correct.

3. Final Answer:

   p.x = 10; -> Option C

4. Quick Check:

   Structure variable assignment uses dot (.) [OK]

Hint: Use dot (.) for struct variables, arrow (->) only for pointers [OK]

Common Mistakes:

• Using arrow (->) with non-pointer variable
• Using colon (:) which is invalid syntax
• Using array-like syntax on struct members

3. What is the output of this code?

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

int main() {
  struct Person p = {"Amy", 25};
  printf("%s %d", p.name, p.age);
  return 0;
}

medium

A. Amy 25

B. Amy 0

C. Error: cannot assign string to array

D. Random garbage values

Solution

1. Step 1: Understand structure initialization

   The structure p is initialized with "Amy" for name and 25 for age.

2. Step 2: Print structure members

   The printf prints p.name as a string and p.age as an integer, so output is Amy 25.

3. Final Answer:

   Amy 25 -> Option A

4. Quick Check:

   Struct initialized correctly, prints members [OK]

Hint: Initialize structs with braces; access members with dot [OK]

Common Mistakes:

• Thinking string assignment to array is invalid here
• Confusing pointer and array initialization
• Expecting syntax error for string in struct

4. Identify the error in this code snippet:

struct Data {
  int id;
  float value;
};

int main() {
  struct Data d;
  d->id = 5;
  d.value = 3.14;
  return 0;
}

medium

A. Using arrow operator (->) with structure variable

B. Missing semicolon after struct definition

C. Incorrect float assignment

D. No error, code is correct

Solution

1. Step 1: Check member access operators

   The variable d is a structure variable, not a pointer, so d->id is incorrect.

2. Step 2: Correct operator usage

   Use dot operator (.) for structure variables: d.id = 5; is correct.

3. Final Answer:

   Using arrow operator (->) with structure variable -> Option A

4. Quick Check:

   Arrow (->) only for pointers, dot (.) for variables [OK]

Hint: Use dot (.) for struct variables, arrow (->) only for pointers [OK]

Common Mistakes:

• Using arrow (->) on non-pointer struct variable
• Ignoring dot operator for member access
• Assuming no error when mixing operators

5. Consider this code:

struct Employee {
  char name[20];
  int id;
};

int main() {
  struct Employee emp1 = {"John", 101};
  struct Employee *ptr = &emp1;
  ptr->id = 202;
  printf("%s %d", emp1.name, emp1.id);
  return 0;
}

What will be the output?

hard

A. John 101

B. John 202

C. Error: cannot use arrow operator here

D. John 0

Solution

1. Step 1: Understand pointer to structure

   ptr points to emp1, so ptr->id changes emp1.id.

2. Step 2: Update and print values

   After ptr->id = 202;, emp1.id becomes 202. Printing emp1.name and emp1.id outputs John 202.

3. Final Answer:

   John 202 -> Option B

4. Quick Check:

   Pointer access updates struct member correctly [OK]

Hint: Use arrow (->) with pointers to structs to access members [OK]

Common Mistakes:

• Thinking arrow operator causes error with pointers
• Not realizing pointer changes original struct
• Confusing dot and arrow operators with pointers