Besides using the C++ components, you probably should change your use of pointers. 

When you first declare the pointer it points to some random spot in memory, that something else could be using. Then when you asign that memory location the value of 20 it will overwrite the previous value. Because the memory wasn't "yours" to begin with, it could mess things up, even if it looks like there were no compilation errors. 

Instead use one of these options:

int *n = (int*)malloc(sizeof(int)); //here you allocate memory to store an interger in and you have your pointer point to it.

*n = 20; //now you can use the pointer to access and change to value stored at that spot in memory

or

int a = 7; //when you declare a normal variable memory gets allocated automatically

int *n = &a; //you can now create a pointer that points to the same spot in memory

*n = 20; //and you can change the value stored there

-sorry if this wasn't the clearest explanation, but if you really want to learn all this you should just watch the videos on pointers and

dynamic memory management