5.23

              }

       }

       return count;

}

int main()

{

       string sentence;

       cout<<"请输入一条英文语句：";

       getline(cin,sentence);

       int letter_count = count_letters(sentence);

       cout<<"这条英文中字母的个数为："<<letter_count<<endl;

       return 0;

}

6-22

void reverse(string &s)

{

       int left = 0,right = s.length() - 1;

       while(left<right)

       {

              swap(s[left],s[right]);

              left++;

              right--;

        }

}

6-23

#include<iostream>

#define N 8

using namespace std;

int main()

{

       int a[N];

       int b=0;

       cout<<"请输入N个人的考试成绩"<<endl;

       for(int i=0;i<N;i++)

       {

              cin>>a[i];

              b+=a[i];

       }

       double c=b/8.000;

       cout<<"这些同学的平均成绩为："<<c<<endl;

       return 0;

}