hdu 2399 GPA

題意：

#include
#include
#include
using namespace std;

int main(){
    string str;
    while(getline(cin,str)){
        int num = 0;
        double sum = 0;
        for(int i=0;i
 
 
 
 
GPA
平均績點
Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 3137    Accepted Submission(s): 1867





Problem Description
Each course grade is one of the following five letters: A, B, C, D, and F. (Note that there is no grade E.) 
每一門課程的成績用分別用A，B，C，D，F表示。（注意這裡沒有E）
The grade A indicates superior achievement , whereas F stands for failure. 
A表示成績優秀，F表示不及格。
In order to calculate the GPA, the letter grades A, B, C, D, and F are assigned the following grade points, respectively: 4, 3, 2, 1, and 0.


 為了計算GPA，A，B，C，D，F分別代表4，3，2，1，0個學分。


Input
The input file will contain data for one or more test cases, one test case per line. 
輸入文件將包含多組測試事件，每一個事件一行。
On each line there will be one or more upper case letters, separated by blank spaces.
 在每一行將會有一個或多個大寫字母，每兩個字母之間用空格表示。


Output
Each line of input will result in exactly one line of output. 
對於每一行輸入，恰好用一行輸出。
If all upper case letters on a particular line of input came from the set {A, B, C, D, F} 
所有的輸入字母都是大寫，
then the output will consist of the GPA, displayed with a precision of two decimal places. 
然後輸出GPA，結果精確到兩位小數。
Otherwise, the message "Unknown letter grade in input" will be printed.
 否則，輸出提示信息“ Unknown letter grade in input ”；


Sample Input
A B C D F
B F F C C A
D C E F


Sample Output
2.00
1.83
Unknown letter grade in input


Author 2006Rocky Mountain Warmup

Source HDU “Valentines Day” Open Programming Contest 2009-02-14