TYBcs OS-Syspro Slip 7-1 | IProgramX

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

typedef struct node
{
char line[80];
struct node *next;
}NODE;

NODE *first,*last;
int len,changed;

NODE * get_node(char *s)
{
NODE *p;
p=(NODE*)malloc(sizeof(NODE));
strcpy(p->line,s);
p->next=NULL;
return p;
}

void create(char fname[])
{
NODE *p;
FILE *fp;
char buff[80];

fp = fopen(fname,"r");
if(fp==NULL)
{
printf("File %s not found.\n",fname);
exit(1);
}

while(fgets(buff,80,fp)!=NULL)
{
p = get_node(buff);

if(first==NULL)
first = p;
else
last->next = p;

last = p;
len++;
}

fclose(fp);
}

void append()
{
NODE *p;
char buff[80];

printf("Enter text (type END to stop):");

fflush(stdin);
fgets(buff,80,stdin);

while(strcmp(buff,"END\n")!=0)
{
p = get_node(buff);
if(first==NULL)
first = p;
else
last->next = p;
last=p;
len++;

fflush(stdin);
fgets(buff,80,stdin);
}

changed=1;
}

void print()
{
NODE *p;
int i=1;

p=first;
while(p!=NULL)
{
printf("%d:%s",i,p->line);
i++;
p=p->next;
}
}

void del(int pos)
{
NODE *p,*q;
int i=1;

p = q = first;
while(i<pos)
{
q = p;
p = p->next;
i++;
}

if(p==first)
{
first = p->next;
}
else if(p==last)
{
q->next=NULL;
last=q;
}
else
{
q->next=p->next;
}

free(p);
len--;
changed=1;
}

int main(int argc, char *argv[])
{
char buff[80],ch,fname[30]="";
int n;

if(argc==2)
{
strcpy(fname,argv[1]);
create(fname);
}

while(1)
{
printf("$");
fflush(stdin);
fgets(buff,80,stdin);

sscanf(buff,"%c %d",&ch,&n);

switch(ch)
{
case 'a':
append();
break;
case 'p':
print();
break;
case 'd':
if(n>=1 && n<=len)
del(n);
else
printf("Invalid position: %d\n",n);
break;
case 'e':
exit(0);
default:
printf("Invalid command.\n");
}
}

return 0;
}