Call by reference :
In this method of passing the structures to functions, the address of a structure variable /object is passed to the function using address of (&) operator. So any change made to the contents of structure variable inside the function are reflected back to the calling function.
#include< iostream >
using namespace std;
struct Employee {
char name[50];
int age;
float salary;
};
void readData(Employee&);
void printData(Employee);
int main()
{
Employee p;
readData(p );
printData(p );
return 0;
}
cout << "Enter Full Name:";
cin.get(p.name,50);
cout << "Enter age:";
cir >> p.age;
cout << "Enter salary:";
cin >> p.salary:
}
void printData(Employee p)
{
cout << "\nDisplaying Information." << endl;
cout << "Name: " << p.narne << endl;
cout << "Age:" << p.age << endl;
cout << " Salary: " << p.salary;
}
Output.
Enter Full name: Kumar
Enter age: 55
Enter salary: 34233.4
Displaying Information.
Name: Kumar
Age: 55
Salary: 34233.4

Call by value:
When a structure is passed as argument to a function using call by value method, any change made to the contents of the structure variable inside the function to which it is passed do not effect the structure variable used as an argument.
Consider this example:
#include< iostream >
useing namespace std;
struct Employee
{
char name[50];
int age;
float salary;
};
void printData(Employee); //Function declaration
int main()
{
Employee p;
cout << "Enter Full name:";
cin >> p.name;
cout << "Enter age:";
cin >> p.age;
cout << "Enter salary:"; .
cin >> p.salary,
//Function call with structure variable as
an argument
PrintData(P);
return ();
}
void printData(Employee q)
{
cout << "\nDisplaying Information. " << endl;
cout << "Name:" << q.name << endl;
cout << "Age:" << q.age << endl;
cout << '' Salary: " << q.salary:
}
Output:
Enter Full name: Kumar
Enter age: 55
Enter salary: 34233.4
Displaying Information.
Name: Kumar
Age: 55
Salary: 34233.4

An array of structures is declared in the same way as declaring and array with built-in data types like int or char. A class may contain many students. So, the definition of structure for one student can also be extended to all the students. If the class has 20 students, then 20 individual structures are required. For this purpose, an array of structures can be used
The following program read the details of 20 students and prints the same.
#include< iostream >
using namespace std;
struct Student
{
int age;
float height, weight;
char name[30];
};
void main()
{
Student std[20];
int i;
cout << "Enter the details for 20 students" << endl;
for(i=0;i<20;i++ )
cout << " Enter the details of student'' << i+ 1<< endl;
cout << " Enter the age:"<< endl;
cin >> std[i].age;
cout << "Enter the height:" << endl;
cin >> std[i].height;
cout << "Enter the weight" << endl;
cin >> std[i].weight;
}
cout << "The values entered for Age, height and weight are''< for(i=0;i<20;i++ )
cout << "Student'' << i+ 1<< "\t" << std[i].age << "\
cout << "std[i].height << "\t" << std[i].weight;
}

In C++, arrays can be passed to a function as an argument. To pass an array to a function in C++, the function needs the array name as an arugment. Passing a two-dimensional array to a function a program to display marks of 5 students by passing one dimensional array to a function
# include< iostream >
using namespace std;
void display (in m[5]);
int main()
{
int marks [5]= {88, 76, 90, 61, 69};
display(marks);
return 0;
}
void display (int m[5])
{
cout << "\n Display Marksr:" << endl;
for(int i=0; i<5; i++)
{
cout << "Student'< }
}
Output:
Display Marks:
Student 1: 88
Student 2: 76
Student 3: 90
Student 4: 61
Student 5: 69

#include<iostream>
#include<conio.h>
using namespace std;
int main()
{
int arr1[3][3], arr2[3][3], arr3[3][3], sub, i, j;
cout<<"Enter 3*3 Array 1 Elements:";
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
cin>>arr1[i][j];
}
}
cout<<"Enter 3*3 Array 2 Elements:";
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
cin>>arr2[i][j];
}
}
cout<<"Subtracting array (array l-array2)..."<<endl;
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
arr3[i][j]-arr1[i][j]-arr2[i][j];
}
}
cout<<"Result of Array 1 - Array2 is:"<<endl;
for(i=0; i<3; i++)
{
for(j=0; j<3; j++)
{
cout<<arr3[i][i]<<"\";
}
}
return 0;
}
Output
Enter 3*3 Array 1 Elements:
10 11 12
13 14 15
16 17 18
Enter 3*3 Array 2 Elements:
123
456
789
Subtracting array(array1-array2)
Result of Array 1 -  Array 2 is:
9 9 9
9 9 9
9 9 9