C Program suddenly exits after first input when using printf() - c

Question

I tried this code but after entering the first input it exits. This code works fine though when the printf("hello world"); is commented out or deleted. The compiler doesn't explain anything and it doesn't show any error so I dont know the solution. What is the reason behind this?
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <conio.h>
#include <stdbool.h>
bool login(bool logStatus) // takes in loggedIn value
{
char correctUsername[16] = "admin";
char correctPassword[16] = "admin123";
char *inputUsername;
char *inputPassword;
int i, checkUsername, checkPassword;
printf("Enter your username : \n");
fgets(inputUsername, 16, stdin); /* Get user input for username */
inputUsername[strlen(inputUsername) - 1] = '\0';
// scanf("%s", &inputUsername);
printf("Enter your password : \n");
fgets(inputPassword, 16, stdin); /* Get user input for password */
inputPassword[strlen(inputPassword) - 1] = '\0';
// scanf("%s", &inputPassword);
/* Check username and password */
checkUsername = strcmp(correctUsername, inputUsername);
checkPassword = strcmp(correctPassword, inputPassword);
printf("%d %d", checkUsername, checkPassword);
if (checkUsername == 0 && checkPassword == 0)
{
printf("\n\nLogged In Successful");
logStatus = true;
return logStatus;
}
else
{
printf("\n\nIncorrect username or password\n");
printf("Enter any key to continue...");
getch();
system("cls");
}
}
int main()
{
int input;
int choice;
bool loggedIn = false;
printf("hello world");
login(loggedIn);
return 0;
}

Answer 1

inputUsername and inputPassword are uninitialized pointers. You then pass them to fgets which attempts to dereference those invalid pointers. Doing so invokes undefined behavior.
Make them arrays like the username/password you're checking against.
char inputUsername[16];
char inputPassword[16];