def int_to_decimal_str(integer):
    """
    Helper to convert integers (representing cents) into decimal currency
    string. WARNING: DO NOT TRY TO DO THIS BY DIVISION, FLOATING POINT
    ERRORS ARE NO FUN IN FINANCIAL SYSTEMS.
    @param integer The amount in cents
    @return string The amount in currency with full stop decimal separator
    """
    int_string = str(integer)
    if len(int_string) <= 2:
        return "0." + int_string.zfill(2)
    else:
        return int_string[:-2] + "." + int_string[-2:]