How do I pass 2 arrays into a function, make the user write something in those 2 arrays, and return both of them to the program in C?

Question

I'm a little new to C programming but have some experience. To test my skills, I was trying to build a Bank management program that allows you to create your account, make deposits/withdrawals, etc. The code that I have so far is:

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

char username[20];
char password[20];

void create_account(char* usrname, char* passwd) {
    printf("==================================CREATE BANK ACCOUNT==================================\n");
    while(1) {
        printf("Enter a username that is less than 20 characters: ");
        scanf("%s", usrname);

        if (strlen(usrname) <= 20)
            break;

        printf("That is not less than 20 characters, try again...\n");
    }

    while(1) {
        printf("Enter a password that is less than 20 characters: ");
        scanf("%s", passwd);

        if (strlen(passwd) <= 20) {
            break;
        }
    }

    printf("Thank you, please sign in now...\n");
    sleep(2);
}

int main(void) {
    create_account(username, password);
    printf("\n%s", username);
    printf("\n%s", password);
    return 0;
}

I am aware that I have no parameters when I'm calling the function in main but that's because I don't know what parameters to pass through in the function declaration/initialization so for now, I keep it blank. My question is how do I pass 2 arrays into a function, ask the user to create a username and password, store it in their respective arrays and return both arrays to the program? I know it has to do something with pointers but don't know what to do. I know there is a way to do this with structures too but I don't know anything about that, unions, typedefs, or anything advanced. I really am a novice so please, if the answer is simple, don't get mad at me. Thanks in advance!

Edit: I've read through everyone's comments and answers and made the necessary changes to the code except for the one where someone mentioned using fgets instead of scanf. I don't really understand what to do so I just left it, despite the fact that he said scanf is just as dangerous as gets. I think I got everything but if someone has something else, please let me know. Thank you everyone.

Answer 1

What you can do is create 2 global arrays :

char username[20];
char password[20];

Note that the variables aren't pointers.

Then in the argument passed to the function create_account, you receive pointers that point to the addresses of the two arrays created :

void create_account(char* usrname, char* passwd) {

      /* code... */
}

Remember, the asterisk means "the contents of address...".

To validate the the user's input, I prefer using an infinte loop. The program will break out of the loop once the user enters a valid username (the same can be done for the password) :

while(1) {
    printf("Enter a username that is less than 20 characters: ");
    scanf("%s", usrname);
    
    if (strlen(usrname) <= 20)
        break;

    printf("That is not less than 20 characters, try again...\n");
}

Finally, in the main function when calling create_account, you pass the array variables :

int main(void) {
    create_account(username, password);
    return 0;
}

Just before the return statement you can print out the entered username and password :

printf("\n%s", username);
printf("\n%s", password);