C++第六章课后习题(2)

6-21 编写一个函数，统计一条英文句子中字母的个数，在主程序中实现输入输出。 解：#include #include using namespace std; int count(char*str) { int i,num=0; for(i=0;str[i];i++) { if((str[i]>='a'&&str[i]<='z')||(str[i]>='A'&&str[i]<='Z')) num++; } return num; }

int main(){ char text[100]; cout<<\输入一个英语句子:\ gets(text); cout<<\这个句子里有\个字母。\}

6-22 编写函数void reverse(string &s)，用递归算法使字符串s倒序。 解：#include #include using namespace std;

string reverse(string & str){ if(str.length()>1){ string sub=str.substr(1,str.length() -2); return str.substr(str.length ()-1,1)+reverse(sub)+str.substr(0,1); }else return str; }

int main(){ string str; cout<<\输入一个字符串:\ cin>>str; cout<<\原字符串为:\ cout<<\倒序反转后为:\ return 0; }

6-23 设学生人数N=8，提示用户输入N个人的考试成绩，然后计算出他们的平均成绩并显示出来。

解：#include #include using namespace std; #define N 8 float grades[N]; int main(){ int i; float total,average; for(i=0;i>grades[i]; } total=0; for(i=0;i

6-24 基于char*设计一个字符串类MyString，并且具有构造函数、析构函数、复制构造函数，重载运算符“+”、“=”、“+=”、“[]”，尽可能完善它，使之能满足各种需要。（运算符重载功能为选做，参见第8章） 解：#include #include using namespace std; class MyString{ public: MyString(); MyString(const char*const); MyString(const MyString&); ~MyString(); char&operator[](unsigned short offset); char operator[](unsigned short offset)const; MyString operator+(const MyString&); void operator +=(const MyString&); MyString&operator =(const MyString&); unsigned short getLen()const{ return itsLen; } const char*getMyString()const{ return itsMyString; }

private: MyString(unsigned short); char*itsMyString; unsigned short itsLen; };

MyString::MyString(){ itsMyString=new char[1]; itsMyString[0]='\\0'; itsLen=0; }

MyString::MyString(unsigned short len){ itsMyString=new char[itsLen+1]; for(unsigned short i=0;i<=len;i++) itsMyString[i]='\\0'; itsLen=len; }

MyString::MyString(const char*const cMyString){ itsLen=strlen(cMyString); itsMyString=new char[itsLen +1]; for (unsigned short i=0;i

MyString::MyString(const MyString&rhs){ itsLen=rhs.getLen(); itsMyString=new char [itsLen +1]; for(unsigned short i=0;i

MyString::~MyString(){ delete[]itsMyString; itsLen=0; }

MyString&MyString::operator =(const MyString&rhs){ if(this==&rhs) return *this; delete[]itsMyString; itsLen=rhs.getLen(); itsMyString=new char[itsLen +1]; for(unsigned short i=0;i

char&MyString::operator [](unsigned short offset){