关于 scanf() 的奇怪跳过

Question

I've been trying out a few things with linked lists, mostly because I wanted to find a way to determine the length of a sequence determined by user input. The problem is

Output in Terminal

[filip@filip PointerCheck]$ ./PointerCheck.o 
Enter number to populate the list..
1 2 3
c
Enter number to populate the list..
Printing...
1 2 3 
3

Why is the second population of the list skipped?

I have tried multiple things and I believe that the problem resides somewhere within the while-loop's condition, concerning scanf();
The list functions should be working properly because a separate call from add_to_list() does actually insert an integer within the list, and print_list() prints all of them. So I guess, it must be the while-loop, specifically scanf();

C Code

void user_input_list(void) {
  int *input = NULL;
  input = (int *) malloc(sizeof(int));
  printf("Enter number to populate the list..\n");
  while (scanf("%d", input)) {
    add_to_list(*input, 1);
  }
}

int main(int argc, char const *argv[]) {
  int i = 0;
  struct node *ptr = NULL;

  user_input_list();

  user_input_list();

  print_list();
  printf("%d\n", lenght_list());

  return 0;
}

Here is the entire file, live [link] and on pastebin

Answer 1

It looks like you are entering a non-numeric character to signal the end of input. But, the first nonmatching character encountered by scanf() is left in the input stream. So, you need to clear the extra characters from the input stream before attempting to read from it again. The standard way to do this is:

int c;

while ((c = getchar()) != '\n' && c != EOF)
    continue;

This discards the characters in the input stream until a newline or EOF is reached. Note that getchar() returns EOF in the event of an error, and a user may also input EOF , so it is necessary to test for it explicitly in order to avoid a possible infinite loop.