What causes this integer pointer reassignment to crash?

int *a = 10;
*a = 100;

int *a = 10;

int *a = malloc(sizeof(int));
*a = 100;

int cell = 10;
int *a = &cell; // a points to address of cell
*a = 100;       // content of cell changed

a = malloc(sizeof(int));

long *a;

a = malloc(sizeof *a);

int *a = 10;

int *a = 10;

int *a = 10;

int *a = 10;

*a = 100;

int *a;
a = malloc(sizeof(int));
*a = 10;
printf("a=%in", *a);
free(a);

int *a = (int *) 10;
*a = 100;

int* a = 10;
*a = 100;

"Pointer-to-int 'a' becomes 10"
"Value-pointed-to-by 'a' becomes 100"

"Value-pointed-to-by 10 becomes 100"

int* ptr = (int*)10;  // You've guessed at a memory address, and probably got it wrong
int* ptr = malloc(sizeof(int)); // OS gives you a memory address at runtime

(int*) a = 10;
(*a) = 100;

(void*) v = NULL;

struct Hello {
    int id;
    char* name;
};

...

struct Hello* hello_ptr = malloc(sizeof Hello);
hello_ptr->id = 5;
hello_ptr->name = "Cheery";

void* malloc(size_t size);

free(hello_ptr);

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