C++ *Structure and Function

In previous tutorial we learnt about structures.

In this tutorial, we will learn we will learn how to pass structures as an argument to the function and how to return the structure from the function.

How to pass structure as an argument to function?

Here we have a function printStudentInfo() which takes structure Student as an argument and prints the details of student using structure varaible. The important point to note here is that you should always declare the structure before function declarations, otherwise you will get compilation error.

Example:

#include <iostream>

using namespace std;

struct Student{
    char stuName[30];
    int stuRollNo;
    int stuAge;
};

voidprintStudentInfo(Student);

int main(){
    Student s;
    cout << "Enter Student Name: ";
    cin.getline(s.stuName, 30);

    cout << "Enter Student Roll No: ";
    cin >> s.stuRollNo;

    cout << "Enter Student Age: ";
    cin >> s.stuAge;

    printStudentInfo(s);

    return 0;
}

void printStudentInfo(Students) {
    cout << "StudentRecord: " << endl;
    cout << "Name: "<< s.stuName << endl;
    cout << "RollNo: "<< s.stuRollNo << endl;
    cout << "Age: " << s.stuAge;
}

p Output :

Enter Student Name: Rohit
Enter Student Roll No: 727344
Enter Student Age: 20
StudentRecord:
Name: Rohit
Roll No: 727344
Age: 20

How to create a structure?

The struct keyword is used to createa structure. The general syntax to create a structure is as shown below:

struct structure Name{
    member1;
    member2;
    member3;
    .
    .
    .
    memberN;
};

---

Structures in C++ can contain two types of members

• Data Member - These members are normal C++ variables. We can create a structure with variables of different data types in C++.
• Member Functions - hese members are normal C++ functions. Along with variables, we can also include functions inside a structure declaration.

Example :

int roll;
int age;
int marks;
void print Details()
{
    cout << "Roll = " << roll << "\n";
    cout << "Age = " << age << "\n";
    cout << "Marks = " << marks;
}

In the above structure, the data members are three integer variables to store roll number, age and marks of any student and the member function is printDetails() which is printing all of the above details of any student.

---

How to declare structure variables?

A structure variable can either be declared with structure declaration or as a separate declaration like basic types.

struct Point {
    int x, y;
}p1;

struct Point {
    int x, y;
};

int main() {
    struct Point p1;
}

Note: In C++, the struct keyword is optional before in declaration of a variable. In C, it is mandatory.

How to initialize structure members?

Structure members cannot be initialized with declaration. For example, the following C program fails in compilation.

But is considered correct in C++11 and above.

struct Point {
    int x = 0; // COMPILER ERROR: cannot initialize members here
    int y = 0; // COMPILER ERROR: cannot initialize members here
};

The reason for above error is simple, when a data type is declared, no memory is allocated for it. Memory is allocated only when variables are created.

Structure members can be initialized using curly braces {}. For example, following is a valid initialization.

struct Point {
 int x, y;
};

int main() {
    struct Point p1 = {0, 1};
}

How to access structure elements?

Structure members are accessed using dot (.) operator.

#include <iostream>

using namespace std;

struct Point {
    int x, y;
};

int main() {
    struct Point p1 = {0, 1};
    p1.x = 20;
    cout << "x = " << p1.x << ",y = " << p1.y;
    return 0;
}

Output:

 x = 10, y = 20