C Structures (CT 101): Complete IOE Notes with Examples

Structure

5 hours | 6 marks

COMPUTER PROGRAMMING (CT 101) – Chapter 8

A Structure in C is a powerful user-defined data type that allows you to group together variables of different data types under a single name. This is incredibly useful for organizing complex data, such as records for a student, employee, or book, making your code cleaner and more logical.

Chapter Information

Chapter 8: Structure (5 hours) – 6 marks

Course: Computer Programming (CT 101), I Year I Part

Description: This guide provides a complete overview of C Structures, covering definition, declaration, arrays of structures, nested structures, and pointers to structures, as per the IOE syllabus.

Credit: Sujan Karki

Chapter 8: Structure

5 hours

6 marks

Detailed Chapter Notes

8.1 Defining, Declaring, Accessing & Initializing Structure Elements

Defining a Structure

You define a structure using the struct keyword. This creates a template but does not allocate memory.

struct student {
    char name[50];
    int roll;
    float marks;
};

Declaring Structure Variables

Once defined, you can create variables of that structure type.

// Method 1: After definition
struct student s1, s2;

// Method 2: With definition
struct employee {
    char name[50];
    int id;
} emp1;

Initializing a Structure

You can initialize a structure’s members at the time of declaration.

struct student s1 = {"John Doe", 101, 85.5};

Accessing Structure Members

Use the dot (.) operator to access individual members of a structure variable.

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

struct student {
    char name[50];
    int roll;
    float marks;
};

int main() {
    struct student s1;
    strcpy(s1.name, "Alice");
    s1.roll = 102;
    s1.marks = 92.0;

    printf("Student Name: %s\n", s1.name);
    printf("Roll Number: %d\n", s1.roll);
    printf("Marks: %.1f\n", s1.marks);
    
    return 0;
}

8.2 Array of Structure

An array of structures is used to store multiple records. Each element of the array is a complete structure.

#include <stdio.h>

struct student {
    char name[50];
    int roll;
};

int main() {
    struct student class[3]; // Array of 3 student structures
    int i;

    // Reading data for 3 students
    for (i = 0; i < 3; i++) {
        printf("\nEnter details for student %d:\n", i + 1);
        printf("Enter name: ");
        scanf("%s", class[i].name);
        printf("Enter roll number: ");
        scanf("%d", &class[i].roll);
    }

    // Displaying data
    printf("\nStudent Information:\n");
    for (i = 0; i < 3; i++) {
        printf("Name: %s, Roll: %d\n", class[i].name, class[i].roll);
    }

    return 0;
}

8.3 Array within Structure

A member of a structure can itself be an array. This is commonly used for strings (character arrays) or to hold multiple values like test scores for a single student.

struct student {
    char name[50]; // Array within structure
    int roll;
    float test_scores[4]; // Array within structure
};

8.4 Structure within Structure (Nested Structure)

You can define a structure as a member of another structure. This is called nesting.

#include <stdio.h>

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

struct Employee {
    char name[50];
    struct Date dob; // Nested structure
};

int main() {
    struct Employee emp1 = {"Bob", {15, 6, 1995}};

    printf("Employee Name: %s\n", emp1.name);
    printf("Date of Birth: %d/%d/%d\n", emp1.dob.day, emp1.dob.month, emp1.dob.year);
    
    return 0;
}

8.5 Structure & Pointer

A pointer can point to a structure variable. To access members of a structure using a pointer, you use the arrow (->) operator instead of the dot operator.

#include <stdio.h>

struct student {
    char name[50];
    int roll;
};

int main() {
    struct student s1 = {"Charlie", 103};
    struct student *ptr; // Pointer to a structure
    
    ptr = &s1; // Store the address of s1 in ptr

    printf("Name using pointer: %s\n", ptr->name);
    printf("Roll using pointer: %d\n", ptr->roll);

    return 0;
}

The expression ptr->name is a convenient shorthand for (*ptr).name.

8.6 Passing Structures to/from Function

Structures can be passed to functions in three main ways:

Passing individual members (by value): Simple but inefficient if you need to pass many members.
Passing the entire structure (by value): A copy of the structure is created. The original structure is not modified. Easy to implement but can be slow for large structures.
Passing a pointer to the structure (by reference): The address of the structure is passed. This is the most efficient method as no copy is made. The function can modify the original structure's data.

Example: Passing Structure by Reference (Pointer)

#include <stdio.h>

struct student {
    char name[50];
    int roll;
};

// Function accepts a pointer to a student structure
void displayStudent(struct student *st) {
    printf("Name: %s\n", st->name);
    printf("Roll: %d\n", st->roll);
}

int main() {
    struct student s1 = {"David", 104};
    
    // Pass the address of the structure
    displayStudent(&s1); 
    
    return 0;
}

PDF Notes

Prepared by: Sujan Karki

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