Malor Mass（分子量）

这道题想了小半天，后来经过大神指点后思路终于通了。

 

Hello everyone ,welcome to our programming match. This is your first task!!An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. The molar mass of an organic compound is the mass of one mole of the organic compound. The molar mass of an organic compound can be computed from the standard atomic weights of the elements.

 

When an organic compound is given as a molecular formula, Dr. CHON wants to find its molar mass. A molecular formula, such as C₃H₄O₃ , identifies each constituent element by its chemical symbol and indicates the number of atoms of each element found in each discrete molecule of that compound. If a molecule contains more than one atom of a particular element, this quantity is indicated using a subscript after the chemical symbol.

In this problem, we assume that the molecular formula is represented by only four elements, `C' (Carbon), `H' (Hydrogen), `O' (Oxygen), and `N' (Nitrogen) without parentheses.

The following table shows that the standard atomic weights for `C', `H', `O', and `N'.

 

Atomic Name	Carbon	Hydrogen	Oxygen	Nitrogen
Standard Atomic Weight	12.01 g/mol	1.008 g/mol	16.00 g/mol	14.01 g/mol

 

For example, the molar mass of a molecular formula C₆H₅OH is 94.108 g/mol which is computed by 6 × (12.01 g/mol) + 6 × (1.008 g/mol) + 1 × (16.00 g/mol).

Given a molecular formula, write a program to compute the molar mass of the formula.

 

Input

Your program is to read from standard input. The input consists of T test cases. The number of test cases T is given in the first line of the input. Each test case is given in a single line, which contains a molecular formula as a string. The chemical symbol is given by a capital letter and the length of the string is greater than 0 and less than 80. The quantity number n which is represented after the chemical symbol would be omitted when the number is 1 (2n99) .

 

Output

Your program is to write to standard output. Print exactly one line for each test case. The line should contain the molar mass of the given molecular formula.

 

Sample Input

 

4 
C 
C6H5OH 
NH2CH2COOH 
C12H22O11

 

Sample Output

 

12.010 
94.108 
75.070 
342.296

题目大意：给出一种物质的分子式（不带括号），求分子量。本题中的分子式只包含4种原子，分别为C,H,O,N，原子量分别为12.01,1.008,16.00,14.01（单位：g/mol）。例如，
C6H5OH的分子量为94.108g/mol。

#include<stdio.h>
#include<string.h>
#define maxn 100
char s[maxn];
double m(char x)
{
    if(x=='C') return 12.01;
    if(x=='H') return 1.008;
    if(x=='O') return 16.00;
    if(x=='N') return 14.01;
}
int main()
{
    int t,i;
    double ans;
    scanf("%d",&t);
    while(t--){
        scanf("%s",s);
        ans=0;
        int n=strlen(s);
        for(int i=0;i<n;i++){
            if(s[i]>='A'&&s[i]<='Z'){  //有三种情况：
            if(s[i+1]>='1'&&s[i+1]<='9'){
                if(s[i+2]>='1'&&s[i+2]<='9'){
                    ans+=m(s[i])*((s[i+1]-'0')*10+(s[i+2]-'0'));  //1、数字部分为两位数
                    i+=2;
                }
                else{
                    ans+=m(s[i])*(s[i+1]-'0');  //数字部分为一位数且不为1
                    i++;
                }
            }
            else{
                ans+=m(s[i]);  //两个字母中间没有数字，如OH
            }
        }
    }
        printf("%.3f\n",ans);
    }
    return 0;
}