int a ;
int Data[a];

cout<<"Enter Array Size :";
cin>>a;
cout<<"Enter Data in Array: ";
for(int i=0;i<=a;i++)
{

cin>>Data[i];
}
for(int j=0;j<=a;j++)
cout<<Data[j];
}

int a;
int* Data = NULL;

cout<<"Enter Array Size :";
cin>>a;

// At runtime, it must be done with the "new" operator
Data = new int[a];

// ....


// When done we must "delete" Data because we used "new" to create it
delete[] Data;