Ultraviolet A 1586-molar mass

#include <cstdio>#include <cstring>int key[5];double value[5]={0,12.01,1.008,14.01,16.00};int T;int num=0,p=0,flag=0;int check(char ch){    switch(ch)    {    case 'C':        return 1;    case 'H':        return 2;    case 'N':        return 3;    case 'O':        return 4;    }}int main(){    int len,i;    scanf("%d",&T);    char str[100];    while(T--)    {        scanf("%s",str);        memset(key,0,sizeof(key));        num=0,p=0,flag=0;        len = strlen(str);        for(i=0; i<len;++i)        {            if(str[i]>='C' && str[i]<='O')            {                if(flag)                {                    if(key[p] >0)                        key[p] += num;                    else                        key[p] = num;                    flag=0; num=0;                }                p = check(str[i]);                if(i==len-1 || (str[i+1]>='C' && str[i+1]<='O'))                   ++key[p];            }            else            {                flag=1;                num = num*10+(str[i]-'0');                if(i == len-1)                {                    if(key[p] >0)                        key[p] += num;                    else                        key[p] = num;                }            }        }        double result=0;        for(i=1;i<=4;++i)        {            result += key[i]*value[i];        }        printf("%.3lf\n",result);    }    return 0;}

Question link: http://uva.onlinejudge.org/index.php? Option = com_onlinejudge & Itemid = 8 & category = 830 & page = show_problem & problem = 4461

Ultraviolet A 1586-molar mass