Segmentation error, C File handling program - c

Question

Easy access program
Using linux first of all. I am trying to make a program that will first sign up a user in case he ain't got an account after that he will be directed to a login screen where he will enter his account details and then will be logged in. After that he will be given options to provide easy access to websites e.t.c. Like if the user enters 1 he will be directed to f.b, 2 for quora and so on. I successfully managed to code the program to the log in phase but i did it in a single function i.e main(), so i thought it would be nice if i had separate functions for performing specific tasks. I have coded it this time in separate functions, but i am getting segmentation error this time when i try to open FILE using fopen(). And also please tell me some way to open a website in a browser using console command. Like we have in windows (start www.facebook.com e.g). Here's the code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct user_data {
char name[50];
unsigned long password;
};
struct user_data new_user; // Will hold the data of new
struct user_data data_ver; // Will hold the data read
void sign_up(void);
void sign_in(void);
int main(void) {
beginning: // Beginning label in case of invalid input
printf("\t\t\t\t WELCOME TO EASY ACCESS APPLICATION");
printf("\n\n\nIf you have an account press 1.\n\nPress 2 for sign up.");
char user_choice; // Wil hold the
// user_choice i.e whether he wants to sign up / sign in
user_choice = getchar();
if (user_choice == '1') {
sign_in(); // In case of 1 goto sign in page
}
else if (user_choice == '2') {
sign_up(); // Opening file);
// In case of 2 goto sign up page
}
else {
printf("Invalid input. Try again.\n\n");
puts("Press any key to continue...");
getchar();
system("clear");
goto beginning;
}
return 0;
}
void sign_up(void) {
FILE *data = fopen("data.txt", "a");
if (data == NULL) {
printf("Unable to open file.");
scanf("%c");
system("clear");
}
system("clear");
printf("\t\t----------------------------\n"
"\t\t| |\n"
"\t\t| SIGN UP PAGE |\n"
"\t\t| |\n"
"\t\t----------------------------");
printf("\n\nName:");
scanf("%c"); // Dummy scanf
gets(new_user.name); // Getting name into the struct
printf("\nPassword.");
scanf("%lu", &new_user.password); // Getting pass into the struct
fprintf(data, "%s %lu\n", new_user.name, new_user.password); //Feeding data into FILE
system("clear");
printf("\n\nSign up complete. :) ");
printf("\n\nYou will now be directed to the sign in page. ");
printf("\nPress any key to contine...");
scanf("%c");
system("clear");
fclose(data);
}
void sign_in(void) {
}
I am getting the error on the first line of sign_up function where i am opening FILE.

Answer 1

scanf("%c") expects a pointer where the read character will be stored. scanf() doesn't know if you provided the pointer, it just read the destination address from the expected stack location. Effectively scanf() takes a random address and writes the character there.
Use getchar(); or char Dummy; scanf("%c",&Dummy);.