Vasilis Code

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#define length 256

//introduce structs used

//Name is a string but number of friends and user id are integers.
struct node
{
  char name[50];
  //int relationships;
  int id;
  struct sn *next;
};



//head and current user structure
struct node *head = NULL;
struct node *current = NULL;

//various variables
int input,username,n2;
int num = 1;

//introduce functions to be used
void new2(int n2);
//void relationship(int n);
void printlist(struct node *n);


int main ()
{


  //do loop with condition for exit. We always need the menu to appear initially
  do
    {
      	//user input menu
      printf ("Select an action:\n");
      printf ("1.Introduce new user\n");
      printf ("2.Introduce social relationship\n");
      printf ("3.Print report of all users\n");
      printf ("4.Exit\n");
      scanf ("%d", &input);
      switch (input){
	  case 1:
    	  new2(num);
    	  num++;
    	  break;
	 //case 2:

	 //break;

    case 3:
    	printlist(head);
    	break;
    case 4:
        printf("bye");
        break;
    default:
        printf("error");
    break;
      }
    }while(input<4);


//Input is number of users
void new2(int n2){
    printf("Insert name: ");
    scanf("%s",username);
    //create a ptr
   struct node *ptr = (struct node*) malloc(sizeof(struct node));

   strcpy(ptr->name,username);
   ptr->id = num;

   //point it to old first node
   ptr->next = head;

   //point first to new first node
   head = ptr;
}
//function to introduce new friend
//void relationship(int num){

}
//function to print all users
void printlist(struct node *n)
{
  while (n != NULL)
  {
     printf(" %s \n", n->name);
     printf(" %d \n",n->id);
     n = n->next;
  }
}




Error:
main.c: In function ‘new2’:
main.c:73:11: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’ [-Wformat=]
     scanf("%s",username);
           ^
main.c:77:21: warning: passing argument 2 of ‘strcpy’ makes pointer from integer without a cast [-Wint-conversion]
    strcpy(ptr->name,username);
                     ^
In file included from main.c:2:0:
/usr/include/string.h:129:14: note: expected ‘const char * restrict’ but argument is of type ‘int’
 extern char *strcpy (char *__restrict __dest, const char *__restrict __src)
              ^
main.c:81:14: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
    ptr->next = head;
              ^
main.c: In function ‘printlist’:
main.c:97:8: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
      n = n->next;
        ^
/var/tmp/ccDeZBQG.o: In function `main':
main.c:(.text+0x6c): undefined reference to `new2'
collect2: error: ld returned 1 exit status