printing with type long - c

Question

I'm working on my school project form data structure and I'm having a problem with the type long.
I want to design a small project like a university registration system.
First the person get to chose if he want to register or exit.
If he want to register then he will enter his name and gpa to select the major that is available based on his gpa and the system will generate an id automatically.
The problem is the id is not incremented correctly.
Additional info:
I'm using doubly linked list structure
#include<stdio.h>
#include<stdlib.h>
#include<conio.h>
#include<string.h>
struct student{
char name[30];
int GPA;
unsigned long ID;
char colloege[100];
student *next, *prev;
};
student *stu, *cur, *head, *tail;
void insertfront();
void displaylist(){
unsigned long id=214000000;
cur=head;
printf(" ");
if(cur==NULL)
printf(" ");
else
while(cur!=NULL){
printf("Name:%s\t",cur->name);
printf("ID:%d\t",cur->ID=id++);
printf("GPA:%d\t",cur->GPA);
printf("Colloege of:%s\t",cur->colloege);
printf("\n");
cur=cur->next;
}
}
void main(){
clrscr();
int x;
printf("\n\t\t\t\t******* King Faisal University *********\n");
while(x!=2){
printf("\n press 1 to insert your information ,press 2 to exit\n");
scanf("%d",&x);
insertfront();
displaylist();
}
stu=NULL;
cur=NULL;
head=NULL;
tail=NULL;
getch();
}
void insertfront(){
int x,c;
stu=(student*)malloc(sizeof(student));
fflush(stdin);
printf("Enter your name:\n");
scanf("%[^\n]%*c",stu->name);
printf("Enter your GPA:\n");
scanf("%ul",&stu->GPA);
printf("\n Available Colloeges\n");
if(stu->GPA>=85)
{
printf("1.Colloege of Medicine\n 2.Colloege of Engenering\n 3.Colloege of Computer Science\n 4.Colloege of Business\n 5.Colloege of Art\n");
printf("Enter the colloege number \n");
scanf("%d",&c);
switch(c){
case 1: strcpy(stu->colloege,"Medicien");break;
case 2: strcpy(stu->colloege,"Engenering");break;
case 3: strcpy(stu->colloege,"Computer Science");break;
case 4: strcpy(stu->colloege,"Business");break;
case 5: strcpy(stu->colloege,"Art");break;
}
}
else if(stu->GPA>=75)
{
printf("1.Colloege of Computer Science\n 2.Colloege of Business\n 3.Colloege of Art\n");
printf("Enter the colloege number\n");
scanf("%d",&c);
switch(c){
case 1: strcpy(stu->colloege,"Computer Science");break;
case 2: strcpy(stu->colloege,"Business");break;
case 3: strcpy(stu->colloege,"Art");break;
}
}
else
strcpy(stu->colloege,"Art");
if(head==NULL)
{
stu->next=NULL;
stu->prev=NULL;
head=stu;
tail=stu;
}
else
{
stu->next=head;
stu->prev=NULL;
head->prev=stu;
head=stu;
}
}

Answer 1

You are using an incorrect conversion in your program
printf("ID:%d\t",cur->ID=id++);
// cur->ID is of type unsigned long
// %d is used for values of type int
To print a value of type long you need to use "%ld" in the printf() conversion
long longvalue = 42;
printf("%ld\n", lonvgalue);
To print a value of type unsigned long you need to use "%lu" in the printf() conversion
unsigned long ulongvalue = 42;
printf("%lu\n", ulongvalue);

Answer 2

In addition to the format specifier being wrong, you have a problem with assigning ID:s.
Your code assigns new ID:s every time you display the list.
I would generate the ID only once for each student record, when the record is created.
So add this in insertfront:
stu->ID=id++;
and change the printing in displaylist to:
printf("ID:%lu\t",cur->ID);
and move the declaration of id either to global scope (outside of any function) or as a static variable inside insertfront:
static unsigned long id=214000000;