紫书——Molar mass UVA - 1586

题解：

改题目要求写出分子式，求出他的mol，由于没有括号，基本都是原题模拟就ok了

我的想法每次把上一个记录下来，然后最后搞最后一个。注意点是两个字母相邻的时候，num为0；因此要分开判断

#include <cstdio>
#include <iostream>
#include <string>
#include <cstring>
#include <algorithm>
#include <map>
#include <cctype>

using namespace std;

map<char,double> mol;

void init(){
	mol['C'] = 12.01;	mol['H'] = 1.008;
	mol['O'] = 16.00;	mol['N'] = 14.01;
} 

int main() {
	//freopen("in.txt","r",stdin);
	//freopen("output.txt","w",stdout);
	init();
	
	int n;
	scanf("%d",&n);
	for(int i = 0; i < n; i++){
		string str;
		cin >> str;
		double sum = 0;
		int num = 0;	//保存数字
		char tmp = str[0];	//保存上一个字母
		int len = str.size();
		for(int i = 1; i < len; i++){
			if(isalpha(str[i])){
				if(!num) sum += mol[tmp];
				else sum += mol[tmp]*num;
				num = 0; tmp = str[i];
			}else{
				if(num) num = num*10+str[i]-'0';
				else num = str[i] - '0';
			}
		} 
		if(isalpha(str[len-1])) sum += mol[tmp];
		else sum += mol[tmp]*num;
		printf("%.3f\n",sum);
	}

	return 0;
}