Lesson 11·C Programming

Structures in C

User-defined composite types for grouping heterogeneous variables

What is a Structure?

A Structure is a user-defined composite data type in C that enables storing multiple related variables of different data types (heterogeneous data) under a single unique name.

The struct keyword is used to declare a structure. The individual variables declared within a structure are known as 'members of the structure.'

Instances of Structure

Structure variables (instances) can be declared in two distinct ways:

Instance 1: Declared with Structure Definition

struct emp_info {
    char emp_id[10];
    char name[100];
    float sal;
} emp;  // Variable created immediately

Instance 2: Declared Separately Later

struct emp_info {
    char emp_id[10];
    char name[100];
    float sal;
};

struct emp_info emp;  // Variable created using tag

Accessing Structure Members

Structure members are accessed using the member operator '.' (known as the dot operator or period operator): Structure_var.member

C Example

#include <stdio.h>

struct comp_info {
    char name[50];
    char addr[100];
} info;

void main() {
    printf("Enter company Name: ");
    scanf("%s", info.name);

    printf("Enter Address: ");
    scanf("%s", info.addr);

    printf("\n\nCompany Name: %s", info.name);
    printf("\nAddress: %s\n", info.addr);
}

Program Output

Enter company Name: TechnoExam
Enter Address: Sangli

Company Name: TechnoExam
Address: Sangli

Array within a Structure

A structure member can itself be an array to hold multiple elements:

C Example

#include <stdio.h>

struct result {
    int rno;
    int marks[3];
} res;

void main() {
    int i, total = 0;

    printf("Enter Roll Number: ");
    scanf("%d", &res.rno);

    printf("Enter 3 subject marks: ");
    for (i = 0; i < 3; i++) {
        scanf("%d", &res.marks[i]);
        total += res.marks[i];
    }

    printf("\nRoll Number: %d", res.rno);
    printf("\nMarks are: ");
    for (i = 0; i < 3; i++) {
        printf("%d ", res.marks[i]);
    }
    printf("\nTotal is: %d\n", total);
}

Program Output

Enter Roll Number: 1
Enter 3 subject marks: 63 66 68

Roll Number: 1
Marks are: 63 66 68
Total is: 197

Array of Structures

An array of structures represents multiple database-style records with identical schemas:

C Example

#include <stdio.h>

struct emp_info {
    int emp_id;
    char name[50];
} emp[2];

void main() {
    int i;

    for (i = 0; i < 2; i++) {
        printf("Enter Employee ID: ");
        scanf("%d", &emp[i].emp_id);
        printf("Enter Employee Name: ");
        scanf("%s", emp[i].name);
    }

    printf("\n--- Employee Directory ---\n");
    for (i = 0; i < 2; i++) {
        printf("ID: %d | Name: %s\n", emp[i].emp_id, emp[i].name);
    }
}

Program Output

Enter Employee ID: 1
Enter Employee Name: ABC
Enter Employee ID: 2
Enter Employee Name: XYZ

--- Employee Directory ---
ID: 1 | Name: ABC
ID: 2 | Name: XYZ

Nested Structures (Structures within Structures)

A structure can be embedded within another structure, forming hierarchical data models accessed via chained dot notation (e.g., outer.inner.field):

C Example

#include <stdio.h>

struct stud_res {
    int rno;
    char std[20];

    struct stud_marks {
        char subj_name[30];
        int subj_mark;
    } marks;
} result;

void main() {
    result.rno = 1;
    result.marks.subj_mark = 85;

    printf("Student Roll No: %d\n", result.rno);
    printf("Subject Marks: %d\n", result.marks.subj_mark);
}

Program Output

Student Roll No: 1
Subject Marks: 85