Structures in C

# CHAPTER 15

Structures in C #

1. Introduction #

2. Learning Objectives #

• Define and declare a structure.

• Access and modify structure members using the dot (.) operator.

• Create arrays of structures.

• Use pointers with structures using the arrow (->) operator.

• Build an Employee Management System.

3. Defining a Structure #

struct Student {
    char name[50];
    int age;
    float gpa;
}; // Don't forget the semicolon!

*Note: This just creates a blueprint. It doesn't allocate memory until you create a variable of this type.*

4. Declaring and Accessing Structure Variables #

#include <stdio.h>
#include <string.h>

struct Student {
    char name[50];
    int age;
    float gpa;
};

int main() {
    // 1. Declare a structure variable
    struct Student s1;

    // 2. Assign values (Must use strcpy for strings!)
    strcpy(s1.name, "Alice");
    s1.age = 20;
    s1.gpa = 3.8;

    // 3. Access values
    printf("Name: %s\n", s1.name);
    printf("Age: %d\n", s1.age);
    printf("GPA: %.1f\n", s1.gpa);

    return 0;
}

5. Initializing Structures #

struct Student s2 = {"Bob", 22, 3.5};

6. Arrays of Structures #

struct Student class[3];

// Initialize first student
strcpy(class[0].name, "Charlie");
class[0].age = 21;
class[0].gpa = 4.0;

7. Pointers to Structures #

struct Student s3 = {"David", 19, 3.2};
struct Student *ptr = &s3;

// Using the arrow operator
printf("Name: %s\n", ptr->name); 
ptr->age = 20; // Updates David's age

8. Mini Project: Employee Management System #

#include <stdio.h>

struct Employee {
    int id;
    char name[50];
    float salary;
};

int main() {
    struct Employee emp[2]; // Array of 2 employees

    printf("=== EMPLOYEE ENTRY ===\n");
    for (int i = 0; i < 2; i++) {
        printf("\nEnter details for Employee %d:\n", i + 1);
        printf("ID: ");
        scanf("%d", &emp[i].id);
        printf("Name: ");
        scanf("%s", emp[i].name);
        printf("Salary: ");
        scanf("%f", &emp[i].salary);
    }

    printf("\n=== EMPLOYEE DATABASE ===\n");
    for (int i = 0; i < 2; i++) {
        printf("ID: %d | Name: %s | Salary: $%.2f\n", 
               emp[i].id, emp[i].name, emp[i].salary);
    }

    return 0;
}

9. Memory-Level Explanation (Struct Padding) #

10. Common Mistakes #

• Forgetting the semicolon after the struct definition closing brace }.

• Assigning strings directly: s1.name = "Alice"; is illegal in C. You must use strcpy(s1.name, "Alice");.

• Using . with pointers: If ptr is a pointer, ptr.age is a syntax error. You must use ptr->age.

11. Exercises #

1. 1. Define a struct Point with x and y integer coordinates. Create two points and write a function to calculate the distance between them.

1. 2. Create a struct Book (title, author, price). Initialize it and print it.

12. MCQ Quiz with Answers #

Q5. Can a structure contain a function? a) Yes b) No, C structures only contain data (unlike C++ classes) Answer: b) No, C structures only contain data (unlike C++ classes)

13. Interview Questions #

• Q: What is structure padding and packing in C?

• Q: Differentiate between the dot (.) operator and the arrow (->) operator.

• Q: Can you nest one structure inside another structure? (Yes).

14. Summary #

15. Next Chapter Recommendation #