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

FILE *fp;
char username[30];
char password[30];
char password2[30];

void enterpw() {

        printf ("\nPassword: ");
        fgets (password, sizeof(password), stdin);

        printf ("Confirm password: ");
        fgets (password2, sizeof(password2), stdin);

        while (strcmp(password, password2)) {
                printf ("\nError: Passwords do not match. Try again.\n");
                enterpw();
        }

}

int main() {

        printf ("\nPlease enter your username: ");
        fgets (username, sizeof(username), stdin);

        enterpw();

        fp = fopen ("user.dat", "a");
        fprintf (fp, "%s%s\n", username, password);
        fclose (fp);

        printf("\nPasswords match. Data written to file.\n\n");
        return 0;

}