how to not display the user input password

On my Windows keyboard, pressing those keys (and all the other non-printing characters such as Insert, Delete. Pgup, PgDn etc) generates two characters of which the first one is either 0x00 or 0xE0.

So to stop them printing an asterisk, we need to trap these two characters and the next character as well.

I've altered the program to deal with that but, if you're using an OS other than Windows or a non-English keyboard, then I can't promise it will work as the keyboard mappings may be different. 

I've also replaced the isalnum() library function with the corresponding bool expression as the former seems to have some issues when passed non-printing characters:

#include "stdio.h"
#include "conio.h"
#include "ctype.h"
int main()
{    
    char password[15]; /* max length 14 characters say */
    int i;
    for(i = 0; i < 15; i++) password[i] = '\0';

    int index = 0;
    int controlKey = 0;
    printf("Enter password : ");
    while(index < 14)
    {
        char ch = getch();
        if (controlKey == 1)
        {
           controlKey = 0;
        }
        else if(ch == 13) /* enter key */
        {
           break;
        }
        else if (ch == 8) /* backspace key */
        { 
           if (index > 0)
           {
              putchar(8);
              putchar('\0');
              putchar(8);
              index--;
              password[index] = '\0';
           }
        }
        else if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || (ch >= '0' && ch <= '9'))
        {      
           putchar('*');
           password[index] = ch; 
           index++;
        }
        else if (ch == 0 || ch == -32 )
        {
           controlKey = 1;
        }
    }
     
    printf("\nYour password is %s\n\n", password);
    return 0;
}