C Structures struct, typedef, Nested Structs: Tutorial, Examples, FAQs & Interview Tips

What is a Structure?

A struct (structure) is a user-defined data type that groups variables of different types under a single name. Structures are ideal for representing real-world entities like students, employees, or products.

// Define a structure
struct Student {
    char name[50];
    int  age;
    float gpa;
};

// Declare a variable
struct Student s1;

// Access members with dot operator
s1.age = 20;
strcpy(s1.name, "Alice");

// Initialize at declaration
struct Student s2 = {"Bob", 22, 3.8f};

Pointer to Structure

When accessing structure members through a pointer, use the arrow operator -> instead of the dot operator.

struct Student *ptr = &s1;
printf("%s", ptr->name);   // same as (*ptr).name

Basic struct - Student Record

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

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

void printStudent(struct Student s) {
    printf("Name:  %s\n",  s.name);
    printf("Age:   %d\n",  s.age);
    printf("GPA:   %.2f\n", s.gpa);
    printf("Grade: %c\n",  s.grade);
}

int main() {
    struct Student s1;
    strcpy(s1.name, "Alice");
    s1.age   = 20;
    s1.gpa   = 3.85f;
    s1.grade = 'A';

    // Initialize at declaration
    struct Student s2 = {"Bob", 22, 3.2f, 'B'};

    printf("--- Student 1 ---\n");
    printStudent(s1);

    printf("\n--- Student 2 ---\n");
    printStudent(s2);

    printf("\nSize of struct Student: %zu bytes\n", sizeof(struct Student));

    return 0;
}

Array of Structs and Pointer to Struct

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

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

int main() {
    // Array of structures
    struct Employee team[3] = {
        {"Alice", 101, 75000.0f},
        {"Bob",   102, 68000.0f},
        {"Carol", 103, 82000.0f}
    };

    printf("%-10s %5s %10s\n", "Name", "ID", "Salary");
    printf("---------------------------\n");
    for (int i = 0; i < 3; i++) {
        printf("%-10s %5d %10.2f\n",
               team[i].name, team[i].id, team[i].salary);
    }

    // Pointer to struct - use arrow operator ->
    struct Employee *ptr = &team[0];
    printf("\nFirst employee via pointer:\n");
    printf("Name: %s, Salary: %.2f\n", ptr->name, ptr->salary);

    ptr++;  // move to next struct
    printf("Second employee via pointer:\n");
    printf("Name: %s, ID: %d\n", ptr->name, ptr->id);

    return 0;
}

typedef struct and Nested Struct

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

// typedef lets you use the type without 'struct' keyword
typedef struct {
    int day;
    int month;
    int year;
} Date;

typedef struct {
    char name[50];
    Date birthdate;   // nested struct
    float salary;
} Person;

int main() {
    Person p;
    strcpy(p.name, "Alice");
    p.birthdate.day   = 15;
    p.birthdate.month = 6;
    p.birthdate.year  = 1995;
    p.salary = 60000.0f;

    printf("Name:      %s\n", p.name);
    printf("Birthdate: %02d/%02d/%d\n",
           p.birthdate.day, p.birthdate.month, p.birthdate.year);
    printf("Salary:    %.2f\n", p.salary);

    // No need to write 'struct Person' - just 'Person'
    Person p2 = {"Bob", {20, 3, 1990}, 55000.0f};
    printf("\nName: %s, Born: %d\n", p2.name, p2.birthdate.year);

    return 0;
}

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C Structures struct, typedef, Nested Structs: Tutorial, Examples, FAQs & Interview Tips

What is a Structure?

Pointer to Structure

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