Understanding struct in C: A Beginner-Friendly Guide

When learning C programming, you’ll eventually come across the keyword struct. If you're confused about what it does or how to use it, you're not alone—many beginners feel the same way at first. This guide will help you understand what a struct is, why it's useful, and how to use it effectively through simple explanations and code examples.

Tip: You can try out all the code examples in this article using an online compiler like Programiz Online C Compiler. No installation needed!

What is a struct in C?

In simple terms, a struct (short for "structure") is a user-defined data type in C that allows you to group multiple variables of different types under one name.

Think of it like a custom container that holds different pieces of related data.

Why Use struct?

Imagine you’re working with data about a student. A student has a name, ID number, and grade. Without a struct, you'd declare them like this:

char name[50];
int id;
float grade;

But these variables are not grouped together, even though they all describe the same student. With struct, you can organize them neatly:

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

Now you can use a single Student object to access all related fields.

Breaking Down a struct Declaration

Here’s a simple example:

#include <stdio.h>

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

int main() {
    // Declare and initialize a struct variable
    struct Student s1 = {"Alice", 1001, 89.5};
    // Accessing struct members using dot operator
    printf("Name: %s\n", s1.name);
    printf("ID: %d\n", s1.id);
    printf("Grade: %.2f\n", s1.grade);
    return 0;
}

Explanation:

• struct Student { ... }; — This defines a new structure type named Student.
• Inside the curly braces {} are the members (or fields) of the structure.
• struct Student s1 = {...}; — This declares a variable s1 of type struct Student and initializes its members.
• s1.name, s1.id, s1.grade — Access members using the dot (.) operator.

How to Use struct with Functions

Structures can also be passed to and returned from functions:

#include <stdio.h>

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

// Function that takes a struct as parameter
void printStudent(struct Student s) {
    printf("Name: %s, ID: %d, Grade: %.2f\n", s.name, s.id, s.grade);
}

int main() {
    struct Student s1 = {"Bob", 1002, 92.0};
    printStudent(s1);  // Passing struct to a function
    return 0;
}

Using typedef to Simplify Syntax

Typing struct Student every time can be a bit long. You can simplify it using typedef:

#include <stdio.h>

typedef struct {
    char name[50];
    int id;
    float grade;
} Student;

int main() {
    Student s1 = {"Charlie", 1003, 95.0};
    printf("Name: %s, ID: %d, Grade: %.2f\n", s1.name, s1.id, s1.grade);
    return 0;
}

Now you can just use Student instead of struct Student.

Memory Layout (Advanced Tip for the Curious)

Each member in a struct is stored in memory one after the other. There may be padding added by the compiler for alignment purposes. While this isn’t critical to understand right now, it’s helpful to know that structs can affect how memory is laid out.

Practice Exercise

Try creating your own struct for the following:

• A Book with fields: title, author, and price
• A Car with fields: brand, model, and year

Add a function to print the details of each.

Conclusion

The struct keyword in C helps you organize data more cleanly and logically. It’s especially useful when dealing with complex data that naturally belongs together. Mastering structs will make your C programs more efficient and easier to understand.