3.9—字符串—Valid Number

描述
Validate if a given string is numeric.
Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true
Note: It is intended for the problem statement to be ambiguous. You should gather all requirements
up front before implementing one.

#include
#include 
#include 
using namespace std;
bool ValidNum(string str)
{
	bool flag = false;
	int posindex = 0;
	int negindex = 0;
	int dotindex = 0; int dotcount = 0;
	int eindex = 0; int ecount = 0;
	int length = str.size();
	for (int i = 0; i= 1)
				return flag;
		}
		if (str[i] == '-')
		{
			negindex = i;
			if (negindex >= 1)
				return flag;
		}
		//===
		if (str[i] == '.')
		{
			dotindex = i;
			if (dotindex == 0)
				return flag;
			dotcount++;
			if (dotcount >= 2)
				return flag;
		}
		else if (str[i] == 'e')
		{
			eindex = i;
			ecount++;
			if (ecount >= 2)
				return flag;
		}
		else if ('0' <= str[i] && str[i] <= '9')
		{

		}
		else
			return flag;
	}
	//===
	if (ecount == 1 && dotcount == 1)
	{
		if (eindex>dotindex)
			return true;
		else
			return flag;
	}
	//===
	return true;
}
int main()
{
	string str = "2.2e10";
	bool flag = ValidNum(str);
	if (flag)
		cout << str << "    is a valid num!" << endl;

}