Structure vs Array in C: Key Differences and Usage

In C, a structure groups different types of variables under one name, while an array stores multiple elements of the same type in a sequence. Structures allow mixed data types and named fields, whereas arrays provide indexed access to homogeneous data.

Quick Comparison

This table summarizes the main differences between structures and arrays in C.

Factor	Structure	Array
Data Types	Can hold different types together	Holds only one type of elements
Access Method	Access by field names	Access by index numbers
Memory Layout	Fields stored sequentially but can have padding	Elements stored contiguously without gaps
Size	Size depends on all fields combined	Size = element size × number of elements
Use Case	Group related but different data	Store list of similar items
Declaration	Uses struct keyword	Uses type with square brackets

Key Differences

Structures in C let you combine variables of different types into one unit. For example, you can store an integer, a float, and a character array together in one struct. This is useful when you want to represent a complex object like a person with a name, age, and height.

On the other hand, arrays hold multiple values of the same type in a fixed-size sequence. You access each element by its index number, starting from zero. Arrays are ideal when you need to store many items of the same kind, like a list of scores or temperatures.

Memory-wise, arrays store elements one after another without gaps, making them efficient for looping and indexing. Structures may have padding bytes between fields to align data properly, which can affect their size. Also, structures use named fields for clarity, while arrays rely on numeric indexes.

Code Comparison

Here is an example showing how to store and print a person's data using a structure in C.

c

#include <stdio.h>

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

int main() {
    struct Person p1 = {"Alice", 30, 5.5f};
    printf("Name: %s\n", p1.name);
    printf("Age: %d\n", p1.age);
    printf("Height: %.1f\n", p1.height);
    return 0;
}

Output

Name: Alice
Age: 30
Height: 5.5

Array Equivalent

To store similar data using arrays, you would need separate arrays for each field and use the same index to access related data.

c

#include <stdio.h>

int main() {
    char names[1][20] = {"Alice"};
    int ages[1] = {30};
    float heights[1] = {5.5f};

    printf("Name: %s\n", names[0]);
    printf("Age: %d\n", ages[0]);
    printf("Height: %.1f\n", heights[0]);
    return 0;
}

Output

Name: Alice
Age: 30
Height: 5.5

When to Use Which

Choose structures when you need to group different types of related data into one object for clarity and easier management. They are perfect for representing real-world entities with multiple attributes.

Choose arrays when you need to store many items of the same type and access them by position, such as lists or sequences. Arrays are simpler and more efficient for homogeneous data.

Key Takeaways

Structures group different data types under one name with named fields.

Arrays store multiple elements of the same type accessed by index.

Use structures for complex objects with mixed data.

Use arrays for lists of similar items needing fast indexed access.

Structures may have padding; arrays are contiguous in memory.