Implementation of the ADT interface linked list of the FIFO queue

Implementation of the ADT interface linked list of the FIFO queue

FIFO. h (Interface)

1 #include "Item.h"
2 void QUEUinit(int);
3 int QUEUempty(void);
4 void QUEUput(Item);
5 Item QUEUget(void);

Item. h (custom type)

1 typedef char Item;

FIFO. c (interface implementation)

 1 #include "FIFO.h" 
2 #include <stdlib.h> 
3 
4 typedef struct STACKnode *link;
 5 struct STACKnode 
6 { 
7     Item item;
 8     link next; 
9 };
10 
11 static link head,tail;
12 static int N=1,N1;
13 
14 static int STACKerror(int i)
15 {
16     if(i)
17         return N<N1?1:0;
18 
19     else 
20         return N>0 ?1:0;
21 }
22 link NEW(Item item, link next)
23 {24     link x = malloc(sizeof *x);
25     x->item=item; x->next=next;
26     return x;27 }
28 void QUEUinit(int  maxN)
29 {
30     N1=maxN;
31     head=NULL;
32 }
33 int QUEUempty(void)
34 {
35     return N;
36 }
37 void QUEUput(Item item)
38 {
39     if(head==NULL)
40     {
41         head=(tail=NEW(item, head));
42         return ;
43     }
44     tail->next=NEW(item, tail->next);
45     tail=tail->next;
46     N++;
47 }
48 Item QUEUget(void)
49 {
50     if(STACKerror(0))
51     {
52         Item item=head->item;
53         link t=head->next;
54         free(head);head=t;
55         N--;
56         return item;
57     }
58     else
59         printf("\nSTACKpop false");
60     return NULL;
61 }

Main. c (main Program)

 1 #include <stdio.h> 
2 #include "FIFO.h" 
3  
4 int main(void) 
5 { 
6     int N; 
7     Item str[11]; 
8     scanf("%s", str); 
9     getchar();
10 
11     N=sizeof(str)/sizeof(str[0]);
12     printf("%d\n",N);
13    
 14     QUEUinit(N);
15     for(int i=0; i<N; i++)
16     {
17         QUEUput(str[i]);
18     }
19     for(int i=0; i<N; i++)
20     {
21         printf("%c",QUEUget());
22     }
23     
24     return 0;
25 }