不太会

请 help format，看看说明。

查看format的帮助或者手册
可以看到例子和解释

下面就是帮助文件里面的解释和举例



The %f format

    In %w.df, w is the total output width, including sign and decimal point,
    and d is the number of digits to appear to the right of the decimal
    point.  The result is right-justified.

    The number 5.139 in %12.2f format displays as

        ----+----1--
                5.14
        

    When d==0, the decimal point is not displayed.  The number 5.14 in
    %12.0f format displays as

        ----+----1--
                   5

    %-w.df works the same way, except that the output is left-justified in
    the field.  The number 5.139 in %-12.2f displays as

        ----+----1--
        5.14



The %g format

    In %w.dg, w is the overall width, and d is usually specified as 0, which
    leaves up to the format the number of digits to be displayed to the
    right of the decimal point.  If d!=0 is specified, then not more than d
    digits will be displayed.  As with %f, a minus sign may be inserted to
    left-justify results.

    %g differs from %f in that (1) it decides how many digits to display to
    the right of the decimal point, and (2) it will switch to a %e format if
    the number is too large or too small.

    The number 5.139 in %12.0g format displays as

        ----+----1--
               5.139

    The number 5231371222.139 in %12.0g format displays as

        ----+----1--
          5231371222

    The number 52313712223.139 displays as

        ----+----1--
         5.23137e+10

    The number 0.0000029394 displays as

        ----+----1--
         2.93940e-06



The %e format

    %w.de displays numeric values in exponential format.  w records the
    width of the format.  d records the number of digits to be shown after
    the decimal place.  w should be greater than or equal to d+7 or, if
    3-digit exponents are expected, d+8.

    The number 5.139 in %12.4e format is

        ----+----1--
          5.1390e+00

    The number 5.139*10^220 is

        ----+----1--
         5.1390e+220