#14Structures, Unions & Enums in C++ | C++ Tutorials for Beginners

Structures

The structure is a user-defined data type that is available in C++. Structures are used to combine different types of data types, just like an array is used to combine the same type of data types.

struct employee
{
    /* data */
    int eId; 
    char favChar; 
    float salary; 
};

int main() {
     struct employee harry; 
     harry.eId = 1;
     harry.favChar = 'c';
     harry.salary = 12;
     cout<<harry.eId<<endl;  // 1
     cout<<<<harry.favChar<<endl; // 'c'
     cout<<<<harry.salary<<endl; // 12
     return 0;
}

Note: by convention Capitalize Name like 'Harry' is used for Class Name and Smaller like 'harry' for structure Name

Use typedef

typedef for inbuilt data type

typedef long long ll
ll number;

typedef for Structure

typedef struct employee
{
    /* data */
    int eId; //4
    char favChar; //1
    float salary; //4
} ep;

used a keyword “typedef” before struct and after the closing bracket of structure, we have written “ep”. Now we can create structure variables without using the keyword “struct” and name of the struct.

int main() {
	// struct employee harry
     ep harry; 
     return 0;
}

Unions

Unions are similar to structures but they provide better memory management then structures.  Unions use shared memory so only 1 variable can be used at a time.

• Memory between variables are shared
• in union, we can use only one variable at a time.
• Previous allocated variable will be deallocated to a garbage value.

union money{
	int rupees; // size 4
	char bitCoin; // size 1
	float pounds; // size 4
}

size of struct = sum of size of all data = 4+1+4 = 9 size of union = maximum data size in union = 4

union money m1;
m1.rupees = 34;
cout<<m1.rupees; // 34
 
m1.bitCoin = 'C'
cout<<m1.bitCoin; // 'C'
cout<<m1.rupees; // Garbage Value

Enumeration

Enums are user-defined types which consist of named integral constants. Enums are used to make the program more readable.

• It is used to assign names to a set of values, making code easier to read and maintain.
• Each name in an enum represents an integer value, starting from 0 by default (unless you explicitly set values).

int main(){
	// value =     0       1       2
    enum Meal{ breakfast, lunch, dinner};
    Meal m = lunch;
    cout<<m1; // 1
    cout<<breakfast // 0
    return 0;
}

#63 C++ Templates: Must for Competitive Programming | C++ Tutorials for Beginners

Class -> Object
Template -> Class>

If we want to make array variable arr with different datatype: int, float, char at same time

class intVector{
int *arr;
...
}
 
class floatVector{
float *arr;
...
}
 
class charVector{
char *arr;
...
}

It violates Don-Not-Repeat (DRY) principle.

Template

template <class T>
class vector{
	T*arr;
	public:
		vector(T*arr){
			// code....
		}
		// other methodes...
}
 
int main(){
vector<int> intVec
vector<char> charVec(4) // constructor invoke
}
 

where T= int, float or char etc.

Template Syntax Through template, we can make class one time, and for different different datatypes class will be automatically formed. and so Templates are sometime called parameterised class.

Why use Template

• To follow DRY principle
• Generic Programming (that is generalization of programming)
• Much use in competitive programming

STL + Template : master or give an edge in competitive programming.