Passing structures to function

 In C, there are two main ways to pass a structure to a function:

1. Pass by Value: Passing a copy of the structure, which doesn’t affect the original structure.
2. Pass by Reference: Passing the address of the structure, allowing modifications to the original structure.

Let’s walk through both methods with examples.

Define the Structure

First, let's define a Student structure that has a name, roll number, and marks:

#include <stdio.h>
#include <string.h>

struct Student {
char name[50];
int rollNumber;
float marks;
};

Passing Structure by Value

When we pass a structure by value, a copy of the structure is passed to the function. Any changes made inside the function won’t affect the original structure.

Example: Passing by Value

void displayStudent(struct Student s) {

    printf("Name: %s\n", s.name);

    printf("Roll Number: %d\n", s.rollNumber);

    printf("Marks: %.2f\n", s.marks);

}

int main() {

    struct Student student1 = {"Alice", 101, 88.5};

    // Pass by value

    displayStudent(student1);

    return 0;

}

In this example:

• displayStudent takes a Student structure as a parameter.
• A copy of student1 is passed to displayStudent, so any changes inside the function won’t affect student1 in main.

void modifyStruct(struct Student s) {

    s.marks = 100;  // Modifies only the copy of the structure

}

int main() {

    struct Student student1 = {"Alice", 101, 88.5};

    modifyStruct(student1);

    // student1.marks is still 88.5, not affected by modifyStruct

  printf("%s %d %f",student1.name,student1.rollNumber,student1.marks);

}

Passing Structure by Reference

When we pass a structure by reference, we pass a pointer to the structure. This allows the function to modify the original structure since it has the address of the structure.

void updateMarks(struct Student *s, float newMarks) {

    s->marks = newMarks; // Use arrow operator to access and modify marks

}

int main() {

    struct Student student1 = {"Alice", 101, 88.5};

    // Display original marks

    printf("Original Marks: %.2f\n", student1.marks);

    // Pass by reference

    updateMarks(&student1, 95.0);

    // Display updated marks

    printf("Updated Marks: %.2f\n", student1.marks);

    return 0;

}

In this example:

• updateMarks takes a Student pointer (struct Student *s) as a parameter.
• We use the arrow operator (->) to access and modify marks via the pointer.
• updateMarks(&student1, 95.0); passes the address of student1 to the function, allowing it to modify student1 directly.

Key Points

1. Pass by Value: Safe but doesn’t modify the original structure. Useful when you don’t need to change the data.
2. Pass by Reference: Efficient for large structures, and it allows modification of the original data. Use when changes need to reflect in the original structure.

Summary Table

Method	Syntax in Function Parameter	Effect
Pass by Value	void func(struct Student s)	Copies the structure, original unchanged
Pass by Reference	void func(struct Student *s)	Passes address, original structure can be modified

Example:Develop a function that takes the two dates as input and compares them. The function should return 1 if date1 is earlier than date2, return 0 if date1 is later than date2. Write code to display whether date1 is earlier, later, or the same as date2 based on the function’s result. ( University Question)

#include <stdio.h>

// Structure to store date

typedef struct {

    int day;

    int month;

    int year;

} Date;

// Function to compare two dates

int compareDates(Date date1, Date date2) {

    // Compare years

    if (date1.year < date2.year)

        return 1;

    if (date1.year > date2.year)

        return 0;

    // Compare months

    if (date1.month < date2.month)

        return 1;

    if (date1.month > date2.month)

        return 0;

    // Compare days

    if (date1.day < date2.day)

        return 1;

    if (date1.day > date2.day)

        return 0;

    // Dates are equal

    return -1;

}

int main() {

    Date date1, date2;

    // Input two dates

    printf("Enter first date (DD MM YYYY): ");

    scanf("%d %d %d", &date1.day, &date1.month, &date1.year);

    printf("Enter second date (DD MM YYYY): ");

    scanf("%d %d %d", &date2.day, &date2.month, &date2.year);

    // Compare dates and display result

    int result = compareDates(date1, date2);

    if (result == 1)

        printf("Date1 is earlier than Date2.\n");

    else if (result == 0)

        printf("Date1 is later than Date2.\n");

    else

        printf("Both dates are the same.\n");

    return 0;

}