Question

So I want to read a file, and i should have 4 functions:
it is the main function

/* Queue functions */

/* Basic type for the queue data structure */
typedef struct queue {
  node *front;          /* Front of the line */
  node *rear;   

    /* Back of the line */
} queue;

---

Sorry, I compiled wrongly, it works now.

Answer 1

For str2card and card2str the prototype and the actual function differ. They must be the same. Probably the same with the other too.

You have prototypes here:

// Utility functions
node_data str2card(char *buf);
char *card2str(node_data c, char *buf);

and later the functions:

/* Convert a string like 14D into a card */
card str2card(char *buf){
...
}
...
/* Given a card c, put a string like 14D in buf representing it.  Good
for printing  */
char *card2str(card c, char *buf){
...
}