C3-UVa1586-Molar mass

平台：

UVa Online Judge

題號：

1586 - Molar mass

題目連結：

https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=448&page=show_problem&problem=4461

題目說明：

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。

範例輸入：

4
C
C6H5OH
NH2CH2COOH
C12H22O11

範例輸出：

12.010
94.108
75.070
342.296

解題方法：

用while循环取数字，组成n位数。

程式碼：

#include <cstdio>
#include <cctype>
#include <cstring>

const int MAXN = 85;
double    q['Z'] = { 0 };

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

int main() {
    setStandard();
    int T = 0;
    scanf("%d", &T);
    while (T--) {
        char formula[MAXN] = "";
        scanf("%s", formula);
        int num = 0;
        double sta = 0.0, sum = 0.0;
        for (int i = 0; i < strlen(formula); ) {
            if (isalpha(formula[i])) {
                sta = q[formula[i++]];
                while (isdigit(formula[i])) {
                    num = num * 10 + formula[i] - '0';
                    i++;
                }
                if (num == 0) {
                    num = 1;
                }
                sum += sta * num;
                num = 0;
            }

        }
        printf("%.3lf\n", sum);
    }
}