Structures in C

A structure is a user-defined data type that groups variables of different data types under a single name. Each variable in a structure is called a member.

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Defining a Structure

struct Student {
    int rollNo;
    char name[50];
    float marks;
};

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Declaring Structure Variables

struct Student s1;                              /* single variable */
struct Student s1, s2, s3;                     /* multiple variables */
struct Student s1 = {101, "Alice", 92.5};     /* with initialisation */

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Accessing Members

Use the dot operator (.) to access structure members.

struct Student s1;
s1.rollNo = 101;
strcpy(s1.name, "Alice");
s1.marks = 92.5;

printf("Roll: %d, Name: %s, Marks: %.1f\n",
       s1.rollNo, s1.name, s1.marks);

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Array of Structures

struct Student class[30];

for (int i = 0; i < 30; i++) {
    scanf("%d %s %f", &class[i].rollNo, class[i].name, &class[i].marks);
}

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Structure and Functions

void display(struct Student s) {
    printf("Roll: %d, Name: %s\n", s.rollNo, s.name);
}

int main() {
    struct Student s1 = {101, "Bob", 88.0};
    display(s1);
    return 0;
}

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Pointer to Structure

Use the arrow operator (->) with a pointer to a structure.

struct Student *ptr = &s1;

ptr->rollNo = 102;
printf("%s\n", ptr->name);

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Nested Structures

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

struct Employee {
    int id;
    char name[50];
    struct Date dob;   /* nested structure */
};

struct Employee e1;
e1.dob.day = 15;
e1.dob.month = 8;
e1.dob.year = 1995;

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sizeof a Structure

printf("%zu\n", sizeof(struct Student));
/* may be larger than sum of members due to padding */