C++ Primer 5th的练习—第五章
Ex_5.5
/*
把数字成绩转换成字母成绩，100分对应A++ 90分对应A 80分对应B
70分对应C 60分对应D <60分对应F
除100分以外，末尾8,9的添加+号，末尾0,1,2的添加-号
*/
#include
#include
#include
#include
using namespace std;
int main()
{
const vector scores = { "F","D","C","B","A","A++" };
//这里之所以倒过来写，便于后面的下标计算
int grade;
string lettergrade;
while (cin >> grade && grade >= 0 && grade <= 100)
{
if (grade < 60)
lettergrade = scores[0];
else
//使用计算下标的方式打打减少代码量
lettergrade = scores[(grade - 50) / 10];
if (grade >= 60 && grade != 100) //不及格的分数不讨论加减号
if (grade % 10 >= 3) {
if (grade % 10 >= 8)
lettergrade += '+'; //这里可用"" 也可用''
}
else
lettergrade += "-";
cout << lettergrade << endl;
}
return 0;
}
Ex_5.6
//使用条件运算符代替上题中的if else语句
#include
#include
#include
using namespace std;
int main()
{
const vector scores = { "F","D","C","B","A","A++" };
int grade;
string lettergrade;
while (cin >> grade && grade >= 0 && grade <= 100)
{
grade < 60 ? lettergrade = scores[0] : lettergrade
= scores[(grade - 50) / 10];
if (grade >= 60 && grade != 100)
grade % 10 >= 8 ? lettergrade += '+' :
grade % 10 <= 2 ? lettergrade += '-' : lettergrade += "";
cout << lettergrade << endl;
}
return 0;
}
Ex_5.9
//使用if语句，统计从cin读入文本中有多少个元音字母
#include
using namespace std;
int main()
{
char ch;
int cnt = 0;
while (cin >> ch)
switch (ch){
case'a': case'A':
case'e': case'E':
case'i': case'I':
case'o': case'O':
case'u': case'U':
++cnt; break;
default:
;
}
cout << "The vowel numbers: " << cnt << endl;
return 0;
}
Ex_5.11
//修改程序，也能统计制表符，空格，换行符的数量
#include
using namespace std;
int main()
{
char ch;
int cnt = 0, spacecnt = 0, tabcnt = 0, linecnt = 0;
//使用cin.get()获取字符，因为cin会忽略\t \n和space
while (cin.get(ch))
switch (ch) {
case'a': case'A':
case'e': case'E':
case'i': case'I':
case'o': case'O':
case'u': case'U':
++cnt; break;
case' ':
++spacecnt; break;
case'\t':
++tabcnt; break;
case'\n':
++linecnt; break;
default:
;
}
cout << "The vowel numbers: " << cnt << endl;
cout << "The space character numbers: " << spacecnt << endl;
cout << "The tab character numbers: " << tabcnt << endl;
cout << "The line character numbers: " << linecnt << endl;
return 0;
}
Ex_5.12
/*
修改程序，使其能统计含有2个字符的字符序列 ff，fl，fi
一个字符只会被统计一次，例如xxxxxxxfflxxxxxxxx
我们统计的结果是 ff一次，fl零次，fi零次
*/
#include
using namespace std;
int main()
{
char prech = '\0', ch; //定义prech记录前一个字符
int ffcnt = 0, flcnt = 0, ficnt = 0;
//使用cin.get()获取字符，因为cin会忽略\t \n和space
while (cin >> ch)
{
//设置一个标记，仅当flag为真时，ch赋给prech
bool flag = true;
if (prech == 'f')
switch (ch)
{
case'f':
++ffcnt;
break;
case'l':
++flcnt;
break;
case'i':
++ficnt;
break;
default:
;
}
if (!flag)
prech = '\0';
else
prech = ch;
}
cout << "The ff charcater numbers: " << ffcnt << endl;
cout << "The fl character numbers: " << flcnt << endl;
cout << "The fi character numbers: " << ficnt << endl;
return 0;
}
Ex_5.14
//查找重复出现单词的最大次数
#include
#include
using namespace std;
int main()
{
//当前字符串，前一个字符串，重复出现次数最多字符串
string currString, preString, maxString;
//当前字符串的次数，次数最多的次数
int currCnt = 0, maxCnt = 0;
while (cin >> currString) {
if (currString == preString) {
++currCnt;
if (currCnt > maxCnt) {
maxCnt=currCnt;
maxString = currString;
}
}
else
currCnt = 1;
preString = currString;
}
if (maxCnt > 1)
cout << "The max repeated string is " << maxString << endl
<< "And the count of the string is " << maxCnt << endl;
else
cout << "No any strings have ever appeared in succession." << endl;
return 0;
}
Ex_5.17
//实现两个vector的逐元素比较，检查一个是否是另一个的前缀
#include
#include
using namespace std;
int main()
{
vector v1 = { 0,1,1,2 };
vector v2 = { 0,1,1,3 };
auto it1 = v1.begin();
auto it2 = v2.begin();
//使用迭代器遍历v1和v2
while (it1 != v1.end() && it2 != v2.end())
{
if (*it1 != *it2) { //当前两个元素不相等，不可能是前缀，直接跳出循环
cout << "v1 and v2 are not prefixes to each other." << endl;
break;
}
++it1;
++it2;
}
if (it1 == v1.end() && it2 != v2.end()) //v1.size() < v2.size()
cout << "v1 is v2's prefix." << endl;
if (it2 == v2.end() && it2 != v2.end()) //v1.size() > v2.size()
cout << "v2 is v1's prefix." << endl;
if (it2 == v2.end() && it2 == v2.end()) //v1.size() = v2.size()
cout << "v1 is equal to v2, and they are prefixes to each other." << endl;
return 0;
}
Ex_5.19
#include
#include
using namespace std;
int main()
{
do {
string str1, str2;
cout << "Please enter two strings:";
cin >> str1 >> str2;
if (str1.size() > str2.size())
cout << "The smaller string is " << str2 << endl;
else
cout << "The smaller string is " << str1 << endl;
} while (cin);
return 0;
}
//或者使用条件运算符，代码更简洁，不过可读性低
do {
string str1, str2;
cin >> str1 >> str2;
cout << ((str1.size() > str2.size()) ? str2 : str1)
<< endl; //注意把整个条件运算符括起来
} while (cin);
Ex_5.20
//从标准输入中读取string对象，直到连续出现两个相同的单词
//或所有单词都读完
#include
#include
using namespace std;
int main()
{
string currStr, preStr;
bool flag = false; //设置一个标记，控制输出流
while (cin >> currStr){
if (currStr == preStr){
flag = true;
cout << currStr << "连续重复出现了2次。" << endl;
break;
}
preStr = currStr;
}
if (!flag)
cout << "没有任何单词是连续重复出现的。" << endl;
return 0;
}
Ex_5.21
//修改上题程序，使其找到的重复单词必须以大写字母开头
#include
#include
#include
using namespace std;
int main()
{
string currStr, preStr;
bool flag = false;
while (cin >> currStr) {
if (!isupper(*currStr.begin()))
continue; //如果首字母不是大写字母，进行下一次迭代
if (currStr == preStr) {
flag = true;
cout << currStr << "连续重复出现了2次。" << endl;
break;
}
preStr = currStr;
}
if (!flag)
cout << "没有任何单词是连续重复出现的。" << endl;
return 0;
}
Ex_5.23
#include
using namespace std;
int main()
{
int v1, v2;
while (cin >> v1 >> v2) {
if (v2 == 0) {
cout << "The divisor can't be zero!" << endl;
return -1;
}
cout << v1 / v2 << endl; //若除数为0，这句并不会被执行
}
return 0;
}
Ex_5.25
#include
#include
using namespace std;
int main()
{
int v1, v2;
while (cin >> v1 >> v2) {
try {
if (v2 == 0) {
throw runtime_error("The divisor can't be zero!");
}
cout << v1 / v2 << endl;
}
catch(runtime_error err){
cout << err.what() << endl; //返回初始化的字符串初始值
cout << "Again? Enter y or n" << endl;
char c;
cin >> c;
if (!cin || c == 'n')
break;
}
}
return 0;
}