Structures:
- Structures / struct is a user-defined data type that enables us to organize and group together variables of the same or different data types under a single unit for the purpose of creating composite data structures.
- We studied in our pervious tutorial about arrays. They hold data with the same data type.
Why do we need struct?
What if we need to store more than one variables with same or different data types? Store name, registration number and marks of students? In arrays, we store only marks of students. But if want to store name and registration number along with marks, we use structures or struct. And variables in structures are called members of that particular struct.struct std{
string name = "John";
string regNo = "21-ComputerSceince";
int marks = "90";
float per = "90.00";
};Note : We declare struct outside the main function.
struct.cpp
#include<iostream>
using namespace std;
struct std{
string name = "John";
string regNo = "21-ComputerSceince";
int marks = "90";
float per = "90.00";
};
int main(){
cout<<"I have constructed a struct."<<endl;
return 0;
}- Arrays : Collection of data values with same data type.
- Struct : Collection of data values with same or different data type.
Accessing members of struct:
We have to create an instance of struct inside main function and then using "." operator, we can access members of struct.struct.cpp
#include<iostream>
using namespace std;
struct std{
string name = "John";
string regNo = "21-ComputerSceince";
int marks = "90";
float per = "90.00";
};
int main(){
struct std std1;
//Accessing member of struct
cout<<std1.name<<endl;
cout<<std1.regNo<<endl;
cout<<std1.marks<<endl;
cout<<std1.per<<endl;
return 0;
}Modifying members of struct:
We can reassign data values to our struct members.struct.cpp
#include<iostream>
using namespace std;
struct std{
string name = "John";
string regNo = "21-ComputerSceince";
int marks = "90";
float per = "90.00";
};
int main(){
struct std std1;
std1.name = "Smith"
cout<<std1.name<<endl;
return 0;
}Actually structures make your code more readable and it makes code easy to manage.
Size of struct:
- Size of struct depends upon the type of variable and number of variables, it is storing.
- If struct has 1 int (4 bytes), 1 char(1 byte) and 1 float(4 bytes), its size would be 9 bytes. You can check it by using sizeof() operator.
Unions:
Syntax of union is same as struct. We use union when we need only one data member at a time. For example, if we have three books, we can read one book at a time. We can use one data member of union at a time.Note : You can not declare functions inside a union.
We can declare union and use its one data member at a time. Unions provide us memory optimization.
If we declare a union and a struct with same data members, memory taken by union will be less.
union.cpp
#include<iostream>
using namespace std;
union opt{
int a;
int b;
int c;
};
int main(){
union opt options;
//Accessing member of struct
options.a = 10;
cout<<options.a<<endl;
}Size of Union:
In this case, size of union will be 4 bytes.union std{
int marks;//4bytes
float per;//4bytes
char grade;//1byte
};Points : Do not forget to put ";" after declaring struct or union.