Size of an array

 If the array is a global, static, or automatic variable (int array[10];), then sizeof(array)/sizeof(array[0]) works

If it is a dynamically allocated array (int* array = malloc(sizeof(int)*10); or void f(int array[])), then you cannot find its size at run-time. You will have to store the size somewhere as explained in the code.
Note that sizeof(array)/sizeof(array[0]) compiles just fine even for the second case, but it will silently produce the wrong result.

Code:

int main()
{
  size_t count=sizeof(int) * BITS_PER_BYTE * sizeof(char);
  char *str=(char*)malloc(count);

   printf(" The size is %d\n",count);
 
   memset (str,0,count);

  getchar();
  return 0;
}