C++Primer第五版——习题答案详解（二）

---

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

第3章 字符串、向量和数组

---

练习3.2
一次读入一整行

#include<iostream>
#include<string>
using namespace std;
int main() {
        string a;
        while (getline(cin, a)) {
               cout << a << endl;
        }
        return 0;
}

一次读入一个词

#include<iostream>
#include<string>
using namespace std;
int main() {
        string a;
        while (cin>>a) {
               cout << a << endl;
        }
        return 0;
}

练习3.4

#include<iostream>
#include<string>
using namespace std;
int main() {
	string a, b;
	cin >> a >> b;
	if (a != b) {
		cout << (a >= b ? a : b);
	}
	return 0;
}

练习3.5

#include<iostream>
#include<string>
using namespace std;
int main() {
	string ans,a;
	while (cin >> a) {
		ans += a;
	}
	cout << ans << endl;
	system("pause");
	return 0;
}

#include<iostream>
#include<string>
using namespace std;
int main() {
	string ans,a;
	while (cin >> a) {
		ans += a;
		ans += " ";
	}
	cout << ans << endl;
	system("pause");
	return 0;
}

练习3.6
利用C++11新特性范围for语句，注意要修改字符串必须加上&引用

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main() {
	string t;
	cin >> t;
	for (auto &i : t) {
		i = 'X';
	}
	cout << t << endl;
	system("pause");
	return 0;
}

练习3.7
改为char后结果一样，因为修改的时候就是按字符修改的。

练习3.8
for循环

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main() {
	string t;
	cin >> t;
	for (int i = 0;i < t.size();i++) {
		t[i] = 'X';
	}
	cout << t << endl;
	system("pause");
	return 0;
}

while循环

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main() {
	string t;
	cin >> t;
	int i = 0;
	while (i < t.size()) {
		t[i] = 'X';
		i++;
	}
	cout << t << endl;
	system("pause");
	return 0;
}

显然已知循环次数，for循环更好用些。

练习3.9
不合法，s是空字符串。

练习3.10

#include<iostream>
#include<string>
#include<cctype>
using namespace std;
int main() {
	string t,ans;
	cin >> t;
	for (char &i : t) {
		if (!ispunct(i)) {
			ans += i;
		}
	}
	cout << ans << endl;
	system("pause");
	return 0;
}

练习3.11
如果循环中修改字符串的值，不合法。

练习3.14

#include<iostream>
#include<vector>
using namespace std;
int main() {
	vector<int> ans;
	int temp;
	while (cin >> temp) {
		ans.push_back(temp);
	}
	return 0;
}

练习3.15

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<string> ans;
	string temp;
	while (cin >> temp) {
		ans.push_back(temp);
	}
	return 0;
}

练习3.17

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<string> ans;
	string temp;
	while (cin >> temp) {
		ans.push_back(temp);
	}
	for (string &i : ans) {
		for (char &j : i) {
			if (islower(j)) {
				j = toupper(j);
			}
		}
		cout << i << endl;
	}
	system("pause");
	return 0;
}

练习3.18
不合法，规定只能对确知已存在的元素执行下标操作！

练习3.19

vector<int> val1{ 42, 42, 42, 42, 42, 42, 42, 42, 42, 42};
vector<int> val2(10,42);
vector<int> val3 = val2;

练习3.20

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<int> t;
	int temp;
	while (cin >> temp) {
		t.push_back(temp);
	}
	int len = t.size();
	for (int i = 0;i < len; i++) {
		cout << t[i] + t[i + 1] << endl;
		i++;
	}
	system("pause");
	return 0;
}

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<int> t;
	int temp;
	while (cin >> temp) {
		t.push_back(temp);
	}
	int len = t.size();
	for (int i = 0;i < len; i++) {
		cout << t[i] + t[len - i - 1] << endl;
		i++;
	}
	system("pause");
	return 0;
}

练习3.23

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<int> res = {1,2,3,4,5,6,7,8,9,10};
	for (auto it = res.begin();it != res.end();it++) {
		*it = (*it) * 2;
	}
	for (auto i : res) {
		cout << i << endl;
	}
	system("pause");
	return 0;
}

练习3.24

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<int> t;
	int temp;
	while (cin >> temp) {
		t.push_back(temp);
	}
	for (auto it = t.begin();it != t.end(); it++) {
		cout << (*it) + *(it+1) << endl;
		it++;
	}
	system("pause");
	return 0;
}

练习3.25

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<unsigned> scores(11, 0);
	unsigned grade;
	while (cin >> grade) {
		if (grade <= 100) {
			auto it = scores.begin();
			++*(it + grade / 10);
		}
	}
	for (auto i : scores) {
		cout << i << endl;
	}
	system("pause");
	return 0;
}

练习3.26
两迭代器不能直接相加。迭代器的运算见P111

练习3.27
a.非法，数组大小应该为常量
b.合法
c.非法，返回值不是常量
d.非法，数组大小开小了

练习3.28
分别为空、0、空、随机值

练习3.29
数组大小不够灵活，不能往其中增加元素

练习3.30
去掉for循环中的等于号

练习3.31

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	int a[10];
	for (int i = 0;i < 10;i++) {
		a[i] = i;
	}
	for (int i = 0;i < 10;i++) {
		cout << a[i] << endl;
	}
	system("pause");
	return 0;
}

练习3.32

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	vector<int> a(10);
	for (int i = 0;i < 10;i++) {
		a[i] = i;
	}
	for (int i = 0;i < 10;i++) {
		cout << a[i] << endl;
	}
	system("pause");
	return 0;
}

练习3.33
不初始化会出现随机数字。

练习3.35

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	int a[10] = { 0,1,2,3,4,5,6,7,8,9 };
	int *p = a;
	for (int i = 0;i < 10;i++) {
		*(a + i) = 0;
	}
	for (int i = 0;i < 10;i++) {
		cout << a[i];
	}
	system("pause");
	return 0;
}

练习3.36

bool isEqual(int a[], int m,int b[],int n) {
	if (m != n) return false;
	for (int i = 0;i < m;i++) {
		if (a[i] != b[i]) {
			return false;
		}
	}
	return true;
}

bool isEqual(vector<int> a, vector<int> b) {
	if (a == b) return true;
	else return false;
}

练习3.37
输出hello但后面跟了乱码，因为没有结束字符

练习3.38
地址相加没有意义

练习3.39

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	string s1 = "A string example";
	string s2 = "A different string";
	if (s1 < s2) cout << "s1<s2";
	else if (s1 == s2)cout << "s1=s2";
	else cout << "s1>s2";
	system("pause");
	return 0;
}

#include<iostream>
#include<vector>
#include<string>
using namespace std;
int main() {
	const char s1[] = "A string example";
	const char s2[] = "A different string";
	if (strcmp(s1, s2) < 0) cout << "s2>s1";
	else if (strcmp(s1, s2) == 0) cout << "s1=s2";
	else cout << "s1>s2";
	system("pause");
	return 0;
}

练习3.40

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
int main() {
	char a[100] = "A example";
	char b[100] = "A string";
	char c[200];
	strcpy_s(c, a);
	char *pc = c;
	while (*pc) {
		cout << *pc;
		pc++;
	}
	cout << endl;

	strcat_s(c, " ");
	pc = c;
	while (*pc) {
		cout << *pc;
		pc++;
	}
	cout << endl;

	strcat_s(c, b);
	pc = c;
	while (*pc) {
		cout << *pc;
		pc++;
	}
	cout << endl;
	system("pause");
	return 0;
}

练习3.41

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
int main() {
	int a[10] = { 0,1,2,3,4,5,6,7,8,9 };
	vector<int> t(begin(a), end(a));
	for (auto i : t) {
		cout << i;
	}
	system("pause");
	return 0;
}

练习3.42

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
int main() {
	vector<int> t(10,1);
	int b[10];
	for (int i = 0;i < 10;i++) {
		b[i] = t[i];
	}
	system("pause");
	return 0;
}

练习3.43

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
int main() {
	int ia[3][4] = {
		{0,1,2,3},
	{4,5,6,7},
	{8,9,10,11}
	};

	for (const int(&i)[4] : ia) {
		for (int j : i) {
			cout << j << " ";
		}
	}
	cout << endl;

	for (size_t i = 0;i < 3;i++) {
		for (size_t j = 0;j < 4;j++) {
			cout << ia[i][j] << " ";
		}
	}
	cout << endl;	

	for (int(*i)[4] = begin(ia);i != end(ia);i++) {
		for (int *j = begin(*i);j != end(*i);j++) {
			cout << *j << " ";
		}
	}
	cout << endl;
	system("pause");
	return 0;
}

练习3.44

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
int main() {
	typedef int int_array[4];
	int ia[3][4] = {
		{0,1,2,3},
	{4,5,6,7},
	{8,9,10,11}
	};

	for (const int_array &i : ia) {
		for (int j : i) {
			cout << j << " ";
		}
	}
	cout << endl;

	for (size_t i = 0;i < 3;i++) {
		for (size_t j = 0;j < 4;j++) {
			cout << ia[i][j] << " ";
		}
	}
	cout << endl;	

	for (int_array *i = begin(ia);i != end(ia);i++) {
		for (int *j = begin(*i);j != end(*i);j++) {
			cout << *j << " ";
		}
	}
	cout << endl;
	system("pause");
	return 0;
}

练习3.45

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
int main() {
	typedef int int_array[4];
	int ia[3][4] = {
		{0,1,2,3},
	{4,5,6,7},
	{8,9,10,11}
	};

	for (auto &row : ia) {
		for (auto &col : row) {
			cout << col << " ";
		}
	}
	cout << endl;

	for (size_t i = 0;i < 3;i++) {
		for (size_t j = 0;j < 4;j++) {
			cout << ia[i][j] << " ";
		}
	}
	cout << endl;	

	for (auto *i = begin(ia);i != end(ia);i++) {
		for (auto *j = begin(*i);j != end(*i);j++) {
			cout << *j << " ";
		}
	}
	cout << endl;
	system("pause");
	return 0;
}