> ## Documentation Index
> Fetch the complete documentation index at: https://learn.acadlink.app/llms.txt
> Use this file to discover all available pages before exploring further.

# Passing Structures to Functions

> Pass by value, pass by reference, and return structures from functions

# Passing Structures to Functions

You can pass a structure to a function the same way you pass any variable. There are three approaches:

1. Pass by Value
2. Pass by Reference (using pointer)
3. Return a structure from a function

***

## 1. Pass by Value

A **copy** of the structure is sent to the function. Changes made inside the function do **not** affect the original.

```c theme={null}
#include <stdio.h>

struct Student {
    char name[20];
    int roll;
    float marks;
};

void display(struct Student s) {
    s.marks = 99.9f;   // modifies only the local copy
    printf("Inside : %s %d %.2f\n", s.name, s.roll, s.marks);
}

int main() {
    struct Student s1 = {"Vishal", 101, 75.5};
    display(s1);
    printf("Outside: %.2f\n", s1.marks);   // original unchanged
    return 0;
}
```

**Output:**

```
Inside : Vishal 101 99.90
Outside: 75.50
```

***

## 2. Pass by Reference (Using Pointer)

The **address** of the structure is sent. Changes made inside the function **do** affect the original. Members are accessed using the **arrow operator** (`->`).

```c theme={null}
#include <stdio.h>

struct Student {
    char name[20];
    int roll;
    float marks;
};

void update(struct Student *s) {
    s->marks = 99.9f;   // modifies the original
}

int main() {
    struct Student s1 = {"Vishal", 101, 75.5};
    update(&s1);   // pass address
    printf("After update: %.2f\n", s1.marks);
    return 0;
}
```

**Output:**

```
After update: 99.90
```

***

## 3. Return a Structure from a Function

```c theme={null}
#include <stdio.h>

struct Student {
    char name[20];
    int roll;
    float marks;
};

struct Student getData() {
    struct Student s = {"Kumar", 102, 80.5};
    return s;
}

int main() {
    struct Student s1 = getData();
    printf("%s - %d - %.2f\n", s1.name, s1.roll, s1.marks);
    return 0;
}
// Output: Kumar - 102 - 80.50
```

***

## Comparison

| Method            | Copies Data | Modifies Original | Speed    |
| ----------------- | ----------- | ----------------- | -------- |
| Pass by Value     | Yes         | No                | Slower   |
| Pass by Reference | No          | Yes               | Faster   |
| Return struct     | Yes         | —                 | Moderate |

**Best practice:** For large structures, always prefer passing by reference using a pointer. Use `const struct Type *ptr` if you want to read without modifying.