def ordinal_number(num):
    """create string with ordinal representation of 
    number given
    """

    # 10 through 20 all get 'th' suffix
    if num >=10 and num <=20:
        suffix = 'th'
    # suffix for all other numbers depends on the last digit in the number
    else:
        last_digit = num % 10
        if last_digit == 1: suffix = 'st'
        elif last_digit == 2: suffix = 'nd'
        elif last_digit == 3: suffix = 'rd'
        else: suffix = 'th'
    return(str(num) + suffix)