前缀式求值 NYOJ128

#include<iostream>
#include<cstdlib>
#include<stack>
#include<cstdio>
#include<cstring>
using namespace std;
char c[1005];

/*int Is(char c)
{
	if(c=='+' || c=='-' || c=='*' || c=='/')
		return 1;
	else
		return 0;
}

float cal(float x1,char c,float x2)
{
	switch(c){
	case'+':return x1+x2;break;
	case'-':return x1-x2;break;
	case'*':return x1*x2;break;
	case'/':return x1/x2;break;
	default: return 0;break;
	}
}

float Eva(char c[],int n)
{
	stack<char> a;
	a.push('#');
	stack<float> b;
	float f,pf;
	int j;
//	cout<<c<<endl;
	int flag = 0;
	for(int i=0; c[i] != '\0'; ++i)
	{
		if(c[i] == 32) ++i;
		if(Is(c[i]))
		{
		//	cout<<c[i]<<endl;
			a.push(c[i]);
			flag = 0;
		}
		else
		{
			char num[30];
			num[0] = '\0';
			for(j=0; c[i] != 32 && c[i] != '\0'; j++)
			{
				num[j] = c[i];
				++i;
			}
			if(c[i] == '\0')
				--i;
			num[j] = '\0';
		//	cout<<num<<endl;
			f = atof(num);
			b.push(f);
			if(flag)
			{
				b.pop();
				pf = b.top();
				b.pop();
				b.push(cal(pf,a.top(),f));
				a.pop();
			}
			pf = b.top();
			flag = 1;
		}
	}
	while(a.top() != '#')
	{
		pf = b.top();
		b.pop();
		f = b.top();
		b.pop();
		b.push(cal(pf,a.top(),f));
		a.pop();
	}
	return b.top();
}*/

/*注释的是自己写的代码，提交就是不能ＡＣ可能是有没有考虑到的情况吧，下边的代码是参考别人的,递归用的非常好，也非常妙！还有就是又学习到了一个函数sscanf(c,"%s",ch);把字符数组里的字符复制到ch中，到空格为止！*/

float Eva()
{
	char ch[20];
	sscanf(c,"%s",ch);
	int len = strlen(ch);
	strcpy(c,c+len+1);
	switch(ch[0])
	{
	case'+':return Eva()+Eva();
	case'-':return Eva()-Eva();
	case'*':return Eva()*Eva();
	case'/':return Eva()/Eva();
	default:return atof(ch);
	}
}

int main()
{
//	freopen("in.txt","r",stdin);

	while(gets(c))
		printf("%.2f\n",Eva());
	return 0;
}