C++Primer第五版——习题答案详解（四）

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习题答案目录：https://www.cnblogs.com/Mered1th/p/10485695.html

第5章 语句

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练习5.9

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	char t;
	int cnt = 0;
	while (cin >> t) {
		if (t == 'a' || t == 'e' || t == 'i' || t == 'o' || t == 'u') {
			cnt++;
		}
	}
	cout << cnt;
	return 0;
}

练习5.10

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	char t;
	int aCnt = 0, eCnt = 0, iCnt = 0, oCnt = 0, uCnt = 0;
	while (cin >> t) {
		switch (t) {
			case'a':
			case'A':
				++aCnt;
				break;
			case'e':
			case'E':
				++eCnt;
				break;
			case'i':
			case'I':
				++iCnt;
				break;
			case'o':
			case'O':
				++oCnt;
				break;
			case'u':
			case'U':
				++uCnt;
				break;
		}
		
	}
	cout << "The number of vowel a(A):" << aCnt << endl;
	cout << "The number of vowel e(E):" << eCnt << endl;
	cout << "The number of vowel i(I):" << iCnt << endl;
	cout << "The number of vowel o(O):" << oCnt << endl;
	cout << "The number of vowel u(U):" << uCnt << endl;
	system("pause");
	return 0;
}

练习5.11
noskipws：no skip whitespace

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	char t;
	int aCnt = 0, eCnt = 0, iCnt = 0, oCnt = 0, uCnt = 0,newlineCnt=0,tabCnt=0;
	while (cin >> noskipws >> t) {
		switch (t) {
			case'a':
			case'A':
				++aCnt;
				break;
			case'e':
			case'E':
				++eCnt;
				break;
			case'i':
			case'I':
				++iCnt;
				break;
			case'o':
			case'O':
				++oCnt;
				break;
			case'u':
			case'U':
				++uCnt;
				break;
			case'\n':
				++newlineCnt;
				break;
			case'\t':
			case'\v':
				++tabCnt;
				break;
		}
		
	}
	cout << "The number of vowel a(A):" << aCnt << endl;
	cout << "The number of vowel e(E):" << eCnt << endl;
	cout << "The number of vowel i(I):" << iCnt << endl;
	cout << "The number of vowel o(O):" << oCnt << endl;
	cout << "The number of vowel u(U):" << uCnt << endl;
	cout << "The number of newline:" << newlineCnt << endl;
	cout << "The number of tab:" << tabCnt << endl;
	system("pause");
	return 0;
}

练习5.12

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	char t,p;
	int ffCnt=0,fiCnt=0,flCnt=0;
	while (cin >> t) {
		if (t == 'f') {
			cin >> p;
			switch (p) {
				case'f':
					++ffCnt;
					break;
				case'l':
					++flCnt;
					break;
				case'i':
					++fiCnt;
					break;
			}
		}
	}
	cout << "The number of ff:" << ffCnt << endl;
	cout << "The number of fl:" << flCnt << endl;
	cout << "The number of fi:" << fiCnt << endl;
	system("pause");
	return 0;
}

练习5.13
a.没有break;
b.case1中包含变量的定义，如果越过case1会出错
c.应该改为case1: case3: case5格式
d.case标签必须是常量表达式，改为const unsigned ival.....

练习5.14

#include<iostream>
#include<string>
#include<vector>
#include<cstdio>
#include<cstdlib>
using namespace std;
int main() {
	string nowString, lastString, resString;
	int nowNum = 1, resNum = -1;
	while (cin >> nowString) {
		if (nowString == lastString) {
			nowNum++;
			if (nowNum > resNum) {
				resString = nowString;
				resNum = nowNum;
			}
		}
		else {
			nowNum = 1;
			lastString = nowString;
		}
	}
	if(resNum > 1) cout << resString << " " << resNum;
	else cout << "None";
	system("pause");
	return 0;
}

练习5.17

#include<iostream>
#include<string>
#include<vector>
using namespace std;
bool compare(vector<int> a, vector<int> b) {
	for (decltype(a.size()) i = 0, Sa = a.size(), Sb = b.size();i != Sa && i!=Sb;++i) {
		if (a[i] != b[i]) {
			cout << "false" << endl;
			return false;
		}
	}
	cout << "true" << endl;
	return true;

}
int main() {
	vector<int> a = { 0,1,1,2 };
	vector<int> b = { 0,1,1,2,3,5,8 };
	vector<int> c = { 0,1,2,5,5 };
	compare(a, b);
	compare(a, c);

	system("pause");
	return 0;
}

练习5.18
a.少了花括号
b.变量申明放在了do的条件部分
c.变量申明必须定义在循环体外

练习5.19

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	string a, b;
	do {
		cout << "Please input two strings:"<<endl;
		cin >> a >> b;
		cout << (a.size() < b.size() ? a : b) << endl;
	} while (cin);
	system("pause");
	return 0;
}

练习5.20

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	string now, pre;
	bool flag = false;
	while (cin >> now) {
		if (now == pre) {
			cout << now <<endl;
			flag = true;
			break;
		}
		else {
			pre = now;
		}
	}
	if (!flag) cout << "None" << endl;
	system("pause");
	return 0;
}

练习5.21

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int main() {
	string now, pre;
	bool flag = false;
	while (cin >> now) {
		if (now == pre) {
			if (!isupper(now[0])) continue;
			cout << now <<endl;
			flag = true;
			break;
		}
		else {
			pre = now;
		}
	}
	if (!flag) cout << "None" << endl;
	system("pause");
	return 0;
}

练习5.22

do{
    int sz=get_size();
}while(sz<=0);

练习5.25

#include<iostream>
#include<string>
#include<vector>
#include<stdexcept>
using namespace std;
int main() {
	int a, b;
	while (cin >> a >> b) {
		try {
			if (b == 0) {
				throw runtime_error("除数不能为0\n");
			}
			else {
				cout << a / b << endl;
			}
		}
		catch (runtime_error err) {
			cout << err.what() << "Try Again? Enter y or n" << endl;
			char c;
			cin >> c;
			if (!cin || c == 'n') {
				break;
			}
		}
	}
	system("pause");
	return 0;
}