what is the difference between these two: 1)int* p = new int[5]; 2)int* p = new int(5);

Answer 1

for none, since both are badly declared.
In managing pointers as to the dynamic memory you can also be assigned to the arrays.

taking the example of the course.

int * p = NULL; // Null pointer initialised
p = new int [20]; // Application Memory
delete [] p; // Remove array pointed to by p

Answer 2

1) here we are dynamically allocating memory for array of 5 integer . each of these are initialized to 0.

2) here we are dynamically allocating memory for an integer which is initialized to 5.

Answer 3

https://stackoverflow.com/questions/13797926/what-does-new-int100-do

see Peopleware's answer. It might the second one.