I am a novice, in fact, I am not very clear about this thing, of course, it is impossible to list all the cases, here I just see their own possible situation to do a summary:
The idea above is that you are paying a value to a variable that should not be assigned, or that you are paying a value to a variable (or constant) that cannot be paid
(1) The simplest and most straightforward error is probably the problem with scanf(). We all know that scanf(“% format “,& Variable), then in addition to the string (you can call & , but not), all input is required & If you lose it, you won’t be able to find it on many compilers when it’s mutated, meaning it’s not wrong, but the reason why it’s wrong is because the input data is written as scanf(“% format “, variable), so you don’t know where the input variable will be stored.
(2) Null pointer assignment.
We know that if a pointer is empty is not directly to his assignment is the cause of null Pointers don’t know what the dow was, so he has no fixed memory, now you give his assignment, popular point to understand is that he don’t know how to save, also don’t know what there is, will not be stored, but now you have a need to let him storage, then it will appear afore-mentioned problems, then the solution is to apply for space (using malloc or new), or you try to avoid him to become a null pointer, or when he has become the possibility of a null pointer, you can discuss separately.
Here are a few examples of what is possible:

int * p = 0;
int * p = 0;
p [0] = 100;
of course, it can’t be that obvious in actual code, this is just one example, may be similar, this is you have a good look at yourself, the above 0 and NULL is actually the same, that is, NULL pointer assignment.

a=(double*)malloc(sizeof(double)*6);
h=……
a[0]=h;
First of all you don’t know if malloc is going to succeed or not and if it fails it happens to return NULL and normally you can allocate this amount of memory and it won’t fail but as you said after a couple of loops you might not be free or you might run out of memory or you might fragment and malloc fails and you don’t know so the exact problem is that you assign a NULL pointer to an exception

The following three Pointers are available online: You can compare them with your own:

1:
ar *p;
p = new char[number];
delete [] p;
…
// always using p….
p = XXX;// access violation

2:
char * p;
memcpy (p, XXX, number); // Access Cheesecake
char *p;
p = new char[number];
delete [] p;
…
delete [] p;// the access violation
0xC0000005: Access Cheesecake error debug —

Added a word no problem: (1) compile time
(2) the runtime is a loop calculation, set breakpoints, before a few cycle are no problem, to which a certain cycle (end of cycle conditions have not reached) will appear these problems.
You must be assigning the null pointer somewhere in the middle of the step.
(3) Array or pointer out of bounds
As long as it is related to memory is basically possible, of course, array or pointer out of bounds, this is also very common, this will not give examples, I believe that everyone can understand what consciousness, also know how to solve, this requires you to be more careful and careful.