char* ptr;
strcpy(ptr, "hello world"); // crash here!

char* ptr;
scanf("%s", ptr); // crash here!

{
  int data = 0;
  int* ptr = &data;
  ...
}

int* ptr = malloc(sizeof(int));

/*** examples of incorrect use of pointers ***/

// 1.
int* bad;
*bad = 42;

// 2.
char* bad;
strcpy(bad, "hello");

/*** examples of correct use of pointers ***/

// 1.
int var;
int* good = &var;
*good = 42;

// 2.
char* good = malloc(5+1); // allocates memory for 5 characters and 1 terminator
strcpy(good, "hello");

int* p1 = NULL; // pointer to nowhere
int* p2;        // uninitialized pointer, pointer to "anywhere", cannot be used yet

char * strcpy ( char * destination, const char * source );

char* ptr = malloc(32);
strcpy(ptr, "hello world");

char str[32];
strcpy(str, "hello world");

char *ptr = malloc(32);
scanf("%31[^n]", ptr);