Password autmoated

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

void main()
{
    int a, b, i, c;
    char un[12], pas[20], unv[12], pasv[18];

    printf("USERNAME AND PASSWORD VALIDATION PROGRAM!");
    printf("\n\n    1. Register\n   2. Login  -  ");
    scanf("%d", &a);

    if (a == 1)
    {
        ab:
        system("cls");
        printf("WELCOME TO REGISTRATION PAGE!");
        printf("\n\n    Username (12 character long): ");
        scanf("%s", un);
        printf("    Pasword (Max 20 character long): ");
        scanf("%s", pas);

        printf("\n Press 1. Login, 2. Register again, 3. Exit: ");
        scanf("%d", &b);

        switch(b)
        {
            case 1: goto xy; break;
            case 2: goto ab; break;
            default: exit(0);
        }
    }
    else
    {
        xy:
        system("cls");
        printf("Enter your username: ");
        for (i=0; i<12; i++)
        {
            unv[i]=getch();
            printf("*");
        }

        if (strmp(un, unv)==0)
        {
            printf("\nUsername accepted!");
            printf("\nEnter your password: ");
            for (i=0; i<18; i++)
            {
                pasv[i]=getch();
                printf("*");
            }
            if (strmp(pasv,pas)==0)
            {
                system("cls");
                printf("Welcome to HCL!!");
            }
            else
            {
                system("cls");
                printf("Wrong Password!\n");
                printf("Press 1. exit, 2. Retry");
                scanf("%d", &c);
                switch(c)
                {
                    case 1: exit(0); break;
                    default: goto xy;
                }
            }
        }
        else
        {
            system("cls");
            printf("Wrong Username!\n");
            printf("Press 1. exit, 2. Retry");
            scanf("%d", &c);
            switch(c)
            {
                case 1: exit(0); break;
                default: goto xy;
            }
        }
    }
}