给定一些数字，任务是识别正数和负数，并打印负数和正数的计数。
先决条件： Flex(快速词法分析器生成器)
例子：
Input : -52
Output :
negative number=-52
number of positive numbers = 0
number of negative numbers = 1
Input : 63
Output :
positive number = 63
number of positive numbers = 0
number of negative numbers = 1
下面是实现程序：
/* Lex program to Identify and Count
Positive and Negative Numbers */
%{
int positive_no = 0, negative_no = 0;
%}
/* Rules for identifying and counting
positive and negative numbers*/
%%
^[-][0-9]+ {negative_no++;
printf("negative number = %s\n",
yytext);} // negative number
[0-9]+ {positive_no++;
printf("positive number = %s\n",
yytext);} // positive number
%%
/*** use code section ***/
int yywrap(){}
int main()
{
yylex();
printf ("number of positive numbers = %d,"
"number of negative numbers = %d\n",
positive_no, negative_no);
return 0;
}
输出： 