问题描述
大家好，您能请我帮忙这个flex程序，因为我对flex环境不熟悉，问题是:
您必须制作一个flex文件，该文件应用于生成将与以下模式匹配的词法扫描器:
双:
它是一串没有任何间隙的字符，由三部分组成:
1.整数部分:它是一串数字(至少一位数字).它不能以0开头，除非字符串的值等于零，所以它只能由一位数字(0)组成.可以选择在字符串前面加上(+)或(-)符号.
2.小数部分:此部分是可选的；它以(.)开头，然后是一串数字(至少一位数字).
3.指数部分:这部分也是可选的，它以(e)或(E)开头，然后以(+)或(-)定义指数的符号，然后是一串数字(至少一位)，字符串不能以(0)开头或等于(0).
.54E4、94.E34、09.45E3、00.43E5、4.53E，24.4E，34.3E0、34.3E09都不是双重的.
2.43E9、34E-9、0E + 24，-24.4，+ 90.000e + 34是双重的."
请帮助.
Hello every body could you plz Help me with this flex program because I am no familiar with flex environment the question is:
"You have to make a flex file, this file should be used to generate a lexical scanner that will match the following patterns:
DOUBLE:
It''s a string of characters without any gaps, it consists of three parts:
1. Integer part: It''s a string of digits (at least one digit). It mustn’t begin with 0 except if the value of the string equal to zero so it has to consist of only one digit (0). Optionally the string can be preceded by (+) or (-) sign.
2. Fractional part: this part is optional; it begins with (.), then a string of digits (at least one digit).
3. Exponential part: this part is also optional, it begins with (e) or (E) then (+) or (-) to define the sign of the exponential, then a string of digits (at least one digit), this string mustn’t begin with (0) or equal to (0).
.54E4, 94.E34, 09.45E3, 00.43E5, 4.53E, 24.4E, 34.3E0, 34.3E09 are not DOUBLE.
2.43E9, 34E-9, 0E+24, -24.4, +90.000e+34 are DOUBLE."
plz help.
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