C++Primer第五版——习题答案详解（五）

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

第6章 函数

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练习6.4

#include<iostream>
using namespace std;
int fact(int x) {
    if (x == 1) return x;
    else return x * fact(x - 1);
}

int main() {
    int x;
    cout << "Please input a number:\n";
    while (cin >> x) {
        int ans = fact(x);
        cout << ans << endl;
    }
    system("pause");
    return 0;
}

练习6.5

#include<iostream>
using namespace std;
int abs(int x) {
    return x >= 0 ? x : (-x);
}

int main() {
    int x;
    cout << "Please input a number:\n";
    while (cin >> x) {
        cout << abs(x) << endl;
    }
    system("pause");
    return 0;
}

练习6.7

size_t count_calls(){
    static size_t ctr=0;
    return ctr++;
}

练习6.10

#include<iostream>
using namespace std;
void swap(int *x, int *y) {
    int temp = *x;
    *x = *y;
    *y = temp;
}

int main() {
    int x, y;
    cin >> x >> y;
    cout << x << y << endl;
    swap(x, y);
    cout << x << y << endl;
    system("pause");
    return 0;
}

练习6.12

void swap(int &x, int &y) {
    int temp = x;
    x = y;
    y = temp;
}

练习6.17
不相同，因为转大写需要修改传入的字符串需要加&

#include<iostream>
#include<cctype>
#include<string>
using namespace std;
bool is_upper(const string s) {
    for (auto i : s) {
        if (isupper(i)) return true;
    }
    return false;
}

void to_upper(string &s) {
    for (auto &i : s) {
        i = toupper(i);
    }
}

int main() {
    string s = "abdcedA";
    if (is_upper(s)) cout << "is upper" << endl;
    else cout << "Not upper" << endl;
    to_upper(s);
    cout << s << endl;
    system("pause");
    return 0;
}

练习6.18

bool compare(matrix &a, matrix &b);
vector<int>::iterator change_val(int a, vector<int>::iterator);

练习6.19
a.不合法
b.合法
c.合法
d.合法

练习6.21

#include<iostream>
#include<cctype>
#include<string>
#include<vector>
using namespace std;
int Big(int x, int *y) {
    return x > *y ? x : *y;
}
int main() {
    int x = 3, y = 2;
    cout << Big(x, &y) << endl;
    system("pause");
    return 0;
}

练习6.22
函数传参必须加引用，不加结果不正确。

#include<iostream>
#include<cctype>
#include<string>
#include<vector>
using namespace std;
void swap(int *&x, int *&y) {
    int *temp = x;
    x = y;
    y = temp;
}
int main() {
    int x = 3, y = 2;
    int *px = &x, *py = &y;
    swap(px, py);
    cout << x << ", " << y << endl;
    cout << *px << ", " << *py << endl;
    system("pause");
    return 0;
}

6.23

#include<iostream>
using namespace std;
void print(const int *pi) {
    cout << *pi << endl;
}
void print(const int *beg, const int *end) {
    while (beg != end) {
        cout << *beg++ << " ";
    }
    cout << endl;
}
void print(const int ia[], size_t size) {
    for (size_t i = 0;i != size;i++) {
        cout << ia[i] << " ";
    }
    cout << endl;
}
void print2(const int (&arr)[2]) {
    for (size_t i = 0;i != 2;i++) {
        cout << arr[i] << " ";
    }
    cout << endl;
}

int main() {
    int i = 0, j[2] = { 0,1 };
    print(&i);
    print(begin(j), end(j));
    print(j, 2);
    print2(j);
    system("pause");
    return 0;
}

练习6.24
如果数组大小小于10，会造成数组越界。除此以外数组不能复制成形参。改成指针或引用。

练习6.25
用命令行当做输入，输入的argv[0]保存程序的名字，后面的才是实参

#include<iostream>
#include<string>
using namespace std;

int main(int argc,char const **argv)
{
    cout << argv[1] << endl;
    cout << argv[2] << endl;
    cout << string(argv[1])+string(argv[2]) << endl;
    system("pause");
    return 0;
}

练习6.26

#include<iostream>
#include<string>
using namespace std;

int main(int argc,char const **argv)
{
    for (int i = 0;i < argc;i++) {
        cout << argv[i] << endl;
    }
    system("pause");
    return 0;
}

练习6.27

#include<iostream>
#include<string>
#include<initializer_list>
using namespace std;
int count_Sum(initializer_list<int> il) {
    int sum = 0;
    for (auto beg = il.begin();beg != il.end();beg++) {
        sum += *beg;
    }
    return sum;
}
int main(int argc,char const **argv)
{
    cout << count_Sum({ 1,2,3,4,5 }) << endl;
    system("pause");
    return 0;
}

练习6.28
string类型

练习6.29
如果实参个数多且占用容量大，用引用更好。

练习6.31
返回的引用是局部对象的引用时无效；返回的常量引用是局部常量对象的引用时。

练习6.32
合法，将数组重置为0-9

练习6.33

#include<iostream>
#include<string>
#include<vector>
using namespace std;
void print(vector<int>::iterator vec_begin, vector<int>::iterator vec_end) {
    if (vec_begin != vec_end) {
        cout << *vec_begin << " ";
        return print(++vec_begin, vec_end);
    }
}
int main(int argc,char const **argv)
{   
    vector<int> vec = { 1,2,3,4,6 };
    print(vec.begin(), vec.end());
    system("pause");
    return 0;
}

练习6.34
如果传入的参数小于0，会一直调用不停止

练习6.35
会一直调用本身，无限循环

练习6.36

string (&fun(int i)[10];

练习6.39
a.合法
b.不合法
c.合法

练习6.40
a.正确
b.错误，一旦某个形参被赋予了默认值，它后面的所有形参都必须有默认值

练习6.41
a.非法，第一个形参没有默认值，必须给实参
b.合法
c.合法，'*'转换为整形

练习6.42

#include<iostream>
#include<string>
#include<vector>
using namespace std;
string make_plural(size_t ctr, const string &word, const string &ending = "s") {
    return (ctr > 1) ? word + ending : word;
}
int main()
{   
    cout << make_plural(2, "success", "es") << endl;
    cout << make_plural(2, "failure") << endl;
    system("pause");
    return 0;
}

练习6.43
a.放在头文件中，内联函数在程序中多个定义必须完全一致。
b.放在头文件中，函数声明。

练习6.44

#include<iostream>
#include<string>
#include<vector>
using namespace std;
inline bool isShorter(const string &s1, const string &s2) {
    return s1.size() < s2.size();
}
int main()
{   
    string s1 = "abc", s2 = "abcd";
    cout << isShorter(s1, s2) << endl;
    system("pause");
    return 0;
}

练习6.46
不能，返回值不是常量表达式

练习6.47
在项目属性中设置命令行/DNDEBUG就不会出现 #ifndef....#endif、assert中的内容。

#include<iostream>
#include<string>
#include<vector>
#include<cassert>
using namespace std;
void read_vi(vector<int>::const_iterator iterator_begin, vector<int>::const_iterator iterator_end) {
#ifndef NDEBUG
    cerr << iterator_end - iterator_begin << __func__ << " " << __FILE__ << " "
        << __LINE__ << " " << __TIME__ << " " << __DATE__ << endl;
#endif // !NDEBUG
    if (iterator_begin != iterator_end) {
        cout << *iterator_begin << " ";
        return read_vi(++iterator_begin, iterator_end);
    }
    else {
        cout << endl;
        return;
    }
}
int main()
{   
    vector<int> v{ 1,2,3,4,5 };
    read_vi(v.begin(), v.end());
    system("pause");
    return 0;
}

练习6.48
合理，输入结束时终止程序

练习6.50
a.非法，二义性
b.匹配void f(int)
c.匹配void f(int,int)
d.匹配void f(double,double)

练习6.53
a.合法
b.合法
c.不合法，重复定义

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int calc(int&, int&);
int calc(const int&, const int&);
char calc2(char*, char*);
char calc2(const char*, const char*);
int calc3(char*, char*);
int calc3(char* const, char* const);
int main()
{   
    calc(1, 2);
    system("pause");
    return 0;
}
int calc(int&a, int&b) {
    return a + b;
}
int calc(const int&a, const int&b) {
    return a + b;
}
char calc2(char *a, char *b) {
    return *a;
}
char calc2(const char *a, const char *b) {
    return *a;
}
int calc3(char *a, char *b) {
    return a - b;
}
int calc3(char* const a, char* const b) {
    return a - b;
}

练习6.54

vector<int(*)(int, int)> vf;

练习6.55

#include<iostream>
#include<string>
#include<vector>
using namespace std;
int add(int a, int b) {
    return a + b;
}
int sub(int a, int b) {
    return a - b;
}
int multi(int a, int b) {
    return a * b;
}
int divide(int a, int b) {
    return a / b;
}
int main()
{   
    vector<int(*)(int, int)> vf{ add,sub,multi,divide };
    for (const auto e : vf) cout << e(4, 2) << endl;
    system("pause");
    return 0;
}