What Is User-Defined Data Structure in C?


Larry Thompson

What Is User-Defined Data Structure in C?

In C programming, a user-defined data structure refers to creating a custom data type that can hold multiple variables of different types. This allows programmers to organize and manipulate related data efficiently. User-defined data structures are constructed using the building blocks provided by the C language, such as arrays, structures, and unions.


An array is a collection of elements of the same type stored in a contiguous memory location. It provides a convenient way to store and access multiple values of the same data type using a single variable name.


int numbers[5]; // Declaring an integer array with 5 elements

Arrays can be used to represent user-defined data structures when all the elements have the same type.


A structure is a composite data type that allows you to combine different types of variables under one name. It enables you to create customized data structures by grouping related variables together.


struct structure_name {
    datatype member1;
    datatype member2;
    // ..


struct person {
    char name[20];
    int age;
    float height;

In this example, we defined a structure called “person” that contains three members: “name” (an array of characters), “age” (an integer), and “height” (a floating-point number).


A union is similar to a structure but it allows different variables to share the same memory location. This means that only one member of a union can hold a value at a time.


union union_name {
    datatype member1;
    datatype member2;
    // .


union data {
    int number;
    char character;

In this example, we defined a union called “data” that can hold either an integer or a character. When a value is assigned to one of its members, the other member will become inactive.

Benefits of User-Defined Data Structures

1. Organization and Clarity

User-defined data structures help organize related data into logical groups, making the code easier to understand and maintain. By grouping variables together, it becomes more apparent how they are related and how they should be used.

2. Reusability

User-defined data structures can be reused in multiple parts of a program or even in different programs altogether. Once defined, they can be instantiated as many times as needed, providing consistency and reducing code duplication.

3. Abstraction

User-defined data structures allow programmers to create abstractions that hide complex implementation details. By encapsulating related variables within a structure or union, the underlying logic can be hidden from other parts of the program, resulting in cleaner and more modular code.


In C programming, user-defined data structures offer a powerful way to organize and manipulate related data efficiently. Arrays, structures, and unions provide flexible building blocks for creating custom data types tailored to specific needs. By leveraging these constructs effectively, programmers can enhance code readability, reusability, and maintainability.

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