One of the crucial part of any kind of computer programming is the memory management. In some of the small or short programs, the effect of sporadic memory management does not seem to have an effect because of the larger memory available in todays computers. But as the program grows larger the effect comes into play.

  Basically, the memory for the variables in a program can be allocated in two ways. One is statically, it means during the program compilation the memory is allocated or the amount of memory is known at compile time and allocated. Another one is dynamically, it means during the program run time the memory is allocated or the amount of memory is known at run time and allocated.

  The normal variable declaration and array declaration in C++ is static memory allocation. The amount of memory required for the program is pre-allocated. For array declaration, for example if we declare 50 character array then we can use optimum of 50 character of an array. What if we want to use more than 50 charaters, there is no way that we can use more than 50 characters for the same array. And the another case what if we use only 20 charaters of the array, definately the memory allocated for 30 characters will be wasted. So, such type of memory allocation seems to be tedious though the case is good for the fixed type of the memory allocation. To overcome such type of problems Dynamic memory allocation DMA  comes into existance. DMA  helps for easier memory menagement. It faciliates us to allocate memory as per our requirements at runtime. For example, if we want to write a program that ranks the students based on the marks obtained by the students then in that scenario we don't have the information that how many students will be there for the processing, the memory allocation for the students must be done dynamically.

  In C++, there are two operators available for the dynamic memory allocation and de-allocation; The new operator for allocation and delete  for the de-allocation.

I) new operator

  The new operator in C++ faciliates for dynamic memory allocation similar to malloc() and calloc() in C. It retrives memory at runtime from the memory heap from OS and returns the address.

The syntax is as follows.

data_type *pointer_variable; //pointer variable declaration

pointer_variable = new data_type; //allocate space for single variable

pointer_variable = new data_type[SIZE]; //allocate memory for  an array of size SIZE

For example:

float *float_ptr; //pointer variable declaration 

float_ptr = new float; //allocates memory for single variable

float_ptr = new float[10]; //allocates memory for array of floating type of size 10

also we can directly write, 

float *fptr = new float[10]; //allocation for floating type array of size 10

float *fptr = new float(10); //allocates for the single floating type variable and initializes the value to 10 

Similarly for the multi dimeansional array,

int *twoD;

twoD = new int[m][4];

int *threeD;

threeD = new int[m][4][5];

it means first index can be either variable or constant but other should be constant.

II)delete operator

The memory allocated during runtime by new operator is reserved even after the variable scope ends or the variable is not needed. There can be lots of memory allocations as the program runs on. So, as we go on allocating memory for variables and leaves them unused, the program may run out of memory and can cause serious problems in the programs. For efficient program to write we need to free the allocated memory for the unused variables which is called memory de-allocation.

  In C++ delete  operator releases the memory from the memory heap that are allocated by new  operator. So the released memory can be reused after then.

The syntax for delete operator:

delete pointer_variable; //deletes or releases single dynamic variable 

delete [] pointer_variable; //deletes or releases dynamically created array

For Example:

float *float_pointer;

float_pointer = new float(10);

.........................................

delete float_pointer;

EXAMPLE:

// program to dynamically read the numbers and find the sum

#include<iostream>
using namespace std;

int main(){
	float *float_pointer; //pointer to hold the array
	float SUM = 0;
	int NUMBER;
	cout<<"Enter the total numbers:"<<endl;
	cin>>NUMBER;
	float_pointer = new float[NUMBER];	//allocating memory for array
	cout<<"Enter all the elements:"<<endl;
	for (int i = 0; i < NUMBER; i++)
	{
		cin>>float_pointer[i];
	}
	for (int i = 0; i < NUMBER; i++)
	{
		SUM += float_pointer[i];
	}
	cout<<"TOTAL SUM ="<<SUM<<endl;
	delete [] float_pointer;
	return 0;
}

 SAMPLE RUN:

Enter the total numbers:

3

Enter all the elements:

2.3

3.3

3.3

TOTAL SUM =8.9