Could someone help me clear some confusions about pointers? in C - c

Question

What i understand right now is.
int a = 100;
int *a_ptr; // creates pointer variable named a_ptr and points to type int
a_ptr = &a; // a_ptr is address of a
*a_ptr = 5; // value of pointer = value of a now set to 5.
What i dont understand is the point of pointers is to occupy the address of another variable as its right value or content isnt it?
if *a_ptr is the value shouldn't it be *a_ptr = &a;?
Thanks

Answer 1

Think of a pointer as a road sign: It tells you where you can find something. Nothing more, nothing less. The value/reason for pointers to exist is because it's a concept that we're actually all too familiar with. C passes everything by value. Let's use a far-fetched analogy that, I believe, will clear a couple of things up for you:
Imagine having been on holiday and telling someone about the hotel you stayed in. Instead of describing it in great detail, you'd give the other person the name, the address, and perhaps some more details that could help someone to find the place. You would not set about describing the entire thing in detail, nor would you tear the hotel down and take it with you, let alone rebuild it every time you tell somebody about it.
Back to C: C passes everything by value. In this analogy, that would be like handing everyone a 1-to-1 scale replica of the hotel you're raving on about. That's expensive, time consuming and really quite annoying. The people you've given a copy of the hotel to can change it, but you'd never know: there's a common starting point (the original hotel), but every copy is independent of one another after that.
Like in real life, you'd simply write the address of the hotel down and give that out to family and friends. That's what C does with pointers: it tells you where you can find something (a struct hotel or int), and others can use that address to travel to it.
The added benefit being that if some of your friends actually pay a visit to that place, they can tell you that it's changed in certain ways: the colour is now green, not blue, the owners have changed, etc...
Using the address allows everyone who has the address to have access to up-to-date information about the place.
If the hotel closes down, the address become pointless, but of course, if someone uses the address you gave them thinking they're going to stay in a great place, they'll get angry. What happens next is hard to predict (Undefined behaviour).
So in resuming:
int x = 123;// a hotel
int *x_address = &x;//an address to the hotel
int *for_friend = &x;
int *friend2 = &x; // you can hand out sever addresses to the same hotel
*x_address += 1; // read this as *(travel to)x_address to arrive at hotel X, and stay += 1 night or something
//friend2 wants to see how many nights were spent in hotel x:
printf("%d\n", *friend2);//124 -> 123 originaly + *x_address += 1
If x goes out of scope, that's the equivalent of the hotel closing. If sombody *x_address (travels to x), then their behaviour is undefined.
I've used different analogies in the past to explain in what way you can look at pointers to make them easier to understand, I've written this a while back, don't know if this makes things any clearer, but I thought I'd just post the link here:
Pointers are easy

Answer 2

if *a_ptr is the value shouldn't it be *a_ptr = &a;?
*a_ptr is the value, but &a is not the value, that is a pointer to the value, so they have different types.
So, the value can be set through the pointer, *a_ptr = a, or the pointer can be set to point at a value, a_ptr = &a.