What Is a User-Defined Data Type?


Angela Bailey

A user-defined data type, also known as a composite data type, is a custom data type that is created by the user in programming languages. It allows programmers to define their own data structures, combining multiple variables of different types into a single entity. This article will explore the concept of user-defined data types and how they can be utilized in various programming languages.

Why Use User-Defined Data Types?

User-defined data types offer several advantages over built-in data types. They provide a way to create complex structures that can represent real-world entities more accurately. By combining multiple variables into a single unit, user-defined data types promote code reusability and modularity.

Defining User-Defined Data Types

To define a user-defined data type, programmers need to use the syntax provided by their programming language. Typically, this involves creating a new structure or class that encapsulates the desired variables.

In C++, for example, you can define a structure using the struct keyword:

#include <iostream>
using namespace std;

struct Person {
    string name;
    int age;
    float height;

Here, we have defined a structure called “Person” that consists of three variables: name (of string type), age (of int type), and height (of float type).

Similarly, in Python, you can define a class:

class Person:
    def __init__(self, name, age, height):
        self.name = name
        self.age = age
        self.height = height

In this example, we have defined a class called “Person” with three attributes: name, age, and height.

Using User-Defined Data Types

Once we have defined a user-defined data type, we can create variables of that type and access their individual members. Let’s continue with the previous examples:

In C++:

int main() {
    Person john;
    john.name = "John Doe";
    john.age = 25;
    john.height = 1.75;

    // Accessing the individual members
    cout << "Name: " << john.name << endl;
    cout << "Age: " << john.age << endl;
    cout << "Height: " << john.height << endl;

    return 0;

In Python:

def main():
    john = Person("John Doe", 25, 1.75)

    # Accessing the individual attributes
    print("Name:", john.name)
    print("Age:", john.age)
    print("Height:", john.height)

if __name__ == "__main__":

In both cases, we create a variable of the user-defined data type (Person) and assign values to its individual members (name, age, height). We can then access these members using the dot notation.

Benefits and Use Cases of User-Defined Data Types

User-defined data types offer several benefits and find applications in various scenarios. Here are a few use cases:

  • Data Modeling: User-defined data types can be used to model real-world entities such as persons, employees, products, etc., by combining relevant attributes into a single structure.
  • Data Organization: They help organize related variables into cohesive units, improving code readability and maintainability.
  • Data Storage: User-defined data types can be utilized to store complex data structures in databases or files, facilitating data retrieval and manipulation.
  • Code Reusability: By encapsulating related variables and operations into a user-defined type, developers can reuse the defined structure or class in multiple parts of their codebase.


In summary, user-defined data types allow programmers to create custom data structures that combine multiple variables into a single entity. By defining their own types, programmers can better represent real-world entities and enhance code modularity and reusability. Whether it's modeling objects, organizing data, or improving code efficiency, user-defined data types play a crucial role in various programming languages.

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