c++怎么判断20道选择题的对错？？

write a program to grade a multiple-choice exam. The exam has 20 questions, each answered with a letter in the range of ‘a’ through ‘f’.
The prog优艾设计网_设计客ram should read the key from input, then read each answer and output the ID number and score. Erroneous input should result in a error message.
Input
The first line of input is the key, consisting of a string of 20 characters.
The remaining lines are exam answers, each of which consists of a student ID number, a space, and a string of characters.
The input ends with 0.
Output
Output the score for each ID number in a sigle line, consisting the ID number, a space, and the score or error message.
Sample Input
Copy sample input to clipboard
abcdefabcdefabcdefab
1234567 abcdefabcdefabcdefab
9876543 abddefbbbdefcbcdefac
5554446 abcdefabcdefabcdef
4445556 abcdefabcdefabcdefabcd
3332221 abcdefghijklmnopqrst
0
Sample Output
1234567 20
9876543 15
5554446 Too few answers
4445556 Too many answers
3332221 Invalid answers