C++ Structures (struct)

Definition: A structure (often called a struct) is a user-defined data type that allows you to group multiple related variables of different data types together into a single, cohesive unit. The individual variables inside a structure are referred to as its members or fields.

Why: While arrays allow you to group multiple values of the same data type, real-world data is rarely uniform. For instance, a student profile requires a combination of text (name), integers (age), and decimals (marks). Structures provide the fundamental blueprint needed to model complex, real-world entities cleanly before transitioning into full Object-Oriented Programming.

Declaration Syntax

To define a structure, use the struct keyword followed by a custom name. Inside the curly braces, list the variables that make up the structure. CRITICAL: You must always terminate a structure definition with a semicolon (;) after the closing brace.

struct StructureName {
    dataType member1;
    dataType member2;
    dataType member3;
};

Example: Modeling a Student Record

The following program defines a Student structure, creates an instance of it, assigns values to its members using the dot (.) operator, and prints the record:

#include <iostream>
#include <string>
using namespace std;

// Defining the structural blueprint
struct Student {
    string name;
    int age;
    float marks;
};

int main() {
    // Creating a structure variable named s1
    Student s1;
    
    // Assigning values to members using the dot operator
    s1.name = "Anu";
    s1.age = 19;
    s1.marks = 88.5f;
    
    // Accessing and displaying structure data
    cout << "Name: " << s1.name << endl;
    cout << "Age: " << s1.age << endl;
    cout << "Marks: " << s1.marks << endl;
    
    return 0;
}

Arrays vs. Structures

Key Notes

• Semicolon Rule: Forgetting the closing semicolon after the struct's closing curly brace (};) is one of the most notorious compiler errors for beginners. Always double-check this layout!
• Arrays of Structures: You can combine these concepts to create arrays of structs. For example, Student classroom[50]; creates a collection of 50 individual student records, which you can easily loop through.
• Struct vs. Class: In C++, structures and classes are almost identical. The only technical difference is access control: members of a struct are **public by default**, meaning they can be modified directly from outside the structure, while members of a class are **private by default**.
• Initialization Shorthand: You can initialize a structure on a single line using brace-enclosed lists matching the declaration order, like this: Student s2 = {"Rohan", 20, 91.2f};.