Function not assigning value properly

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C

This is just a part of my code, I don't get any errors, but it appears that function register_user doesn't assign values properly.

Is it because strcpy(user[n].username, username); and user[n].age = user[n].age + age; are not correct?

I realize that the values could've been easily assigned to with gets(user->username); and scanf("%d", &user->age);, but I'm trying to do it this other way.

What I have tried:

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

typedef struct {
    char username[30];
    int age;
} User;

int functions() {
    int option;
    printf("\n");
    printf("1. Register\n");
    printf("2. Display all users\n");

    printf("Choose a function: ");
    scanf("%d", &option);
    getchar();

    return option;
}

void display_user(const User user) {
    printf("\n");
    printf("Username: %s\n", user.username);
    printf("Age : %d\n", user.age);
}

void register_user(User *user, int n) {
    int i, age;
    char username[30];
    
    printf("\nUsername: ");
    scanf("%s", &username);
    printf("Age : ");
    scanf("%d", &age);

    strcpy(user[n].username , username);
    user[n].age = user[n].age + age;

    printf("\nRegistration complete\n");

    }

void display_all_users(const User user[], const int n) {
    int i;

    for (i = 0; i < n; i++) {
        display_user(user[i]);
    }
}


int main()
{
    User users[100];
    User user;
    int n = 0;

    while (1) {
        int option = functions();

        switch (option) {
            case 1:
                register_user(&user, n);
                users[n++] = user;
                break;
            case 2:
                display_all_users(users, n);
                break;  
            default:
                return 0;
        }
    }

    return 0;
}