UVA_325_Identifying Legal Pascal Real Constants

最新推荐文章于 2019-06-04 19:53:05 发布

原创最新推荐文章于 2019-06-04 19:53:05 发布 · 691 阅读

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#uva #FSA

本文介绍了一个使用 C++ 实现的浮点数字符串合法性检查程序。该程序通过状态机的方式判断输入的字符串是否符合合法浮点数的定义，并能够处理包括正负号、小数点和科学计数法在内的多种情况。

#include<iostream>    
#include<sstream>    
#include<string>    
#include<vector>    
#include<list>    
#include<set>    
#include<map>    
#include<stack>    
#include<queue>    
#include<algorithm>  
#include<bitset>
#pragma warning(disable:4996)    
using std::cin;
using std::cout;
using std::endl;
using std::stringstream;
using std::string;
using std::vector;
using std::list;
using std::pair;
using std::set;
using std::multiset;
using std::map;
using std::multimap;
using std::stack;
using std::queue;
using std::priority_queue;
using std::bitset;
bool check(const string &str)
{
	int state = 0;//当前状态
	for (size_t i = 0; i < str.size(); i++)
	{
		switch (state)
		{
		case 0: 
		{
			if (str[i] == '+' || str[i] == '-' || isdigit(str[i]))
			{
				state = 1;
			}
			else
			{
				return false;
			}
		}break;
		case 1:
		{
			if (isdigit(str[i]))
			{
				;
			}
			else if (str[i] == '.')
			{
				state = 2;
			}
			else if (str[i] == 'E' || str[i] == 'e')
			{
				state = 4;
			}
			else
			{
				return false;
			}
		}break;
		case 2:
		{
			if (isdigit(str[i]))
			{
				state = 3;
			}
			else
			{
				return false;
			}
		}break;
		case 3:
		{
			if (isdigit(str[i]))
			{
				;
			}
			else if (str[i] == 'E' || str[i] == 'e')
			{
				state = 4;
			}
			else
			{
				return false;
			}
		}break;
		case 4:
		{
			if (str[i] == '+' || str[i] == '-' || isdigit(str[i]))
			{
				state = 5;
			}
			else
			{
				return false;
			}
		}break;
		case 5:
		{
			if (isdigit(str[i]))
			{
				;
			}
			else
			{
				return false;
			}
		}break;
		default:return false;
		}
	}
	if (state == 3 || state == 5)
	{
		return true;
	}
	return false;
}
int main()
{
	//freopen("input.txt", "r", stdin);    
	//freopen("output.txt", "w", stdout);
	string str;
	while (cin >> str)
	{
		if (str[0] == '*')
		{
			break;
		}
		cout << str;
		if (check(str))
		{
			cout << " is legal." << endl;
		}
		else
		{
			cout << " is illegal." << endl;
		}
	}
	return 0;
}