uva 325 Identifying Legal Pascal Real Constants

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题目：一个简单的格式分析程序。浮点数的组成规则已知。求是不是正确的数字。有限自动机。

注意：有些情况如没有e的情况，不要忘了考虑

#include <cstdio>#include <string.h>#include <cstdlib>#include <cmath>#include <ctgmath>#include <iostream>#include <vector>#include <algorithm>using namespace std;//理解有限状态机/* pre_num 数分析前状态 sign1 数值部分符号 pre_point 数值部分小数点前 point 小数点 fraction 数值部分小数点后 e 指数符号 sign2 指数部分符号 exp 指数部分的的指数状态 followblack 常数后的空格 error 错误*///cin进行字符变量输入，自动过滤头部空格int main(){enum Status{pre_num,sign1,pre_point,point,fraction,e,sign2,exp,error};char m;char str[1000];//存读入的数字Status state;while(cin >> str && strcmp(str, "*")!=0){int i = 0;m = str[i];state = pre_num;while (m != '\0') {switch (state) {case pre_num:  if(m=='+' || m=='-'){state = sign1;break;}   else if(m>='0' && m<='9'){state = pre_point;break;}   else {state = error;break;}case sign1:    if(m>='0' && m<='9'){state = pre_point;break;}   else {state = error;break;}case pre_point:if(m=='.'){state = point;break;}   if(m=='e' || m=='E'){state = e;break;}//不一定是小数的情况   if(m>='0' && m<='9'){state = pre_point;break;}//123.1情况   else state = error;break;case point:    if(m>='0' && m<='9'){state = fraction;break;}   else state = error;break;case fraction: if(m>='0' && m<='9'){state = fraction;break;}   else if(m=='e' || m=='E'){state = e;break;}   else state = error; break;   case e:        if(m=='+' || m=='-'){state = sign2;break;}   else if(m>='0' && m<='9'){state = exp;break;}   else state = error;break;   case sign2:    if(m>='0' && m<='9'){state = exp;break;}   else state = error;break;case exp:      if(m>='0' && m<='9'){state = exp;break;}   else state = error;break;case error:    goto lable;}m = str[++i];}lable:if (state == error) {printf("%s is illegal.\n",str);}else if(state == fraction || state == exp) printf("%s is legal.\n",str);else printf("%s is illegal.\n",str);}return 0;}

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