C++Prime 第六章前30题-优快云博客

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C++Prime 第六章前30题

练习6.1

实参和形参的区别: 实参是实际提供给函数的参数,实参是形参的初始化值,

练习6.2

(a) 返回类型不符

(b)无返回类型

(c)形参不能重名

(d)函数体必须用括号括起来

练习6.3 练习6.4(稍微一改就行)

#include <iostream>
using namespace std;

long long fact(int n)
{
	if (n == 1)
		return 1;
	return n * fact(n - 1);
}

int main()
{
	cout << fact(5) << endl;
	return 0;
}

练习6.5

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

int absolute(int a)
{
	return abs(a);
}
int main()
{
	cout << absolute(-1) << endl;
	return 0;
}

练习6.6

形参和函数体内定义的变量都是局部变量.局部变量:函数开始时为形参申请存储空间,函数终止时,形参被销毁.

局部静态对象在程序的执行路径第一次经过对象定义语句时初始化,直到程序终止时才被销毁.换句话说,局部静态对象比普通局部变量声明周期长.

#include <iostream>
using namespace std;

int fun(int a)
{
	int b = 2;
	static int c = 1;
	return a + b + c;
}
int main()
{
	cout << fun(1) << endl;
	return 0;
}

练习6.7

#include <iostream>
using namespace std;

int fun()
{
	static int n = -1;
	n++;
	return n;

}
int main()
{
	int i = 0;
	for (i; i < 10; ++i)
		cout << fun() << endl;
	return 0;
}

练习6.8 6.9

略

练习6.10


#include <iostream>
using namespace std;

void Swap(int* a, int* b)
{
	int temp = *a;
	*a = *b;
	*b = temp;
}
int main()
{
	int a = 1, b = 2;
	cout << "a =" << a << ", " << "b = " << b << endl;
	Swap(&a, &b);
	cout << "a =" << a << ", " << "b = " << b << endl;
	return 0;
}

练习6.11

#include <iostream>
using namespace std;

void reset(int &a)
{
	a = 0;
}
int main()
{
	int a = 1;
	cout << "a =" << a << endl;
	reset(a);
	cout <<"After reset: a = "<< a << endl;
	return 0;
}

练习6.12

#include <iostream>
using namespace std;

void Swap(int &a,int &b)
{
	int temp = a;
	a = b;
	b = temp;
}
int main()
{
	int a = 1, b = 2;
	cout << "a =" << a << ", " << "b = " << b << endl;
	Swap(a, b);
	cout << "a =" << a << ", " << "b = " << b << endl;
	return 0;
}

练习6.13

void f(T) 是按值传递 void f(&T) 是按引用传递

练习6.14

形参应该是引用类型: 传递参数太大,按值传递无效率. 或需要对原值修改

按值传递 : 不是上述情况

练习6.15

s是常量引用是因为函数不应对s做任何修改.occurs相反,必须修改.

c无需引用是因为就一个char类型,一个字节,按值传递不会损失什么效率.

s是普通引用的话,要特别注意不要对s修改,其他无差距.

occurs是常量引用则本函数错误.因为++occurs;这一句尝试修改常量值.

练习6.16

就是8个字:尽量使用常量引用.

使用常量引用可以:a)避免对形参无意的修改 b)使得形参可以接受更多类型的实参

练习6.17

#include <iostream>
using namespace std;

bool judge(const string& s)
{
	decltype(s.size()) i;
	for ( i = 0; i < s.size(); ++i)
	{
		if (isupper(s[i]))
			return true;
	}
	return false;
}

void change(string& s)
{
	for (auto beg = s.begin(); beg != s.end(); ++beg)
		if (isupper(*beg))
			*beg = tolower(*beg);
}

int main()
{
	string test;
	while (cin >> test)
	{
		cout << test << endl;
		if (judge(test))
			change(test);
		cout << test << endl;
	}
	return 0;
}

使用形参不同.判断是否有大小写字母的函数,使用常量引用.

练习6.18

(a) bool compare(const matrix& m1,const matrix& m2);

(b) vector<int> change_val(int ,vector<int> );

练习6.19

(a) 不合法.参数数量不匹配

练习6.20

尽量是常量引用,在需要对形参做更改时,再换成普通引用.

练习6.21

#include <iostream>
using namespace std;

int compare(int a, const int* p)
{
	return a > * p ? a : *p;
}

int main()
{
	int n = 2, a = 1;
	int* p = &n;
	cout << compare(a, p) << endl;
	return 0;
}

练习6.22

#include <iostream>
using namespace std;

void Swap(int *p, int* q)
{
	int temp = *p;
	*p = *q;
	*q = temp;
}

int main()
{
	int a = 2, b = 1;
	cout << "a = " << a << ",b = " << b << endl;
	Swap(&a, &b);
	cout << "a = " << a << ",b = " << b << endl;
	return 0;
}

练习6.23

#include <iostream>
using namespace std;

void print(int i);
void print(int(&a)[2]);
void print(int(&a)[10]);
int main()
{
	int i = 0, j[2] = { 0,1 }, k[10] = { 1,2,3,4,5,6,7,8,9,10 };
	print(i);
	print(j);
	print(k);
	return 0;
}
void print(int i)
{
	cout << i << endl;
}
void print(int(&a)[2])
{
	for (auto x : a)
		cout << x << " ";
	cout << endl;
}
void print(int(&a)[10])
{
	for (auto x : a)
		cout << x << " ";
	cout << endl;
}

练习6.24

输出ia数组的元素.存在问题是:传入的ia数组长度并不一定是10个,函数体内可能越界.

修改:

void print(const int ia[10], size_t n)

{

for(size_t i = 0; i < n; ++i)

//同题目给出

}

练习6.25

#include <iostream>
using namespace std;

int main(int argc,char **argv)
{
	string tmp;
	for (int i = 1; i < argc; ++i)
	{
		tmp += argv[i];
		tmp += " ";
	}
	cout << tmp << endl;
	return 0;
}

练习6.26

不会!!!

练习6.27

#include <iostream>
#include <initializer_list>
#include <cstdarg>
using namespace std;

int Sum(initializer_list<int> lst)
{
	int sum = 0;
	for (const auto& x : lst)
		sum += x;
	return sum;
}

int main()
{
	cout << Sum({ 1,2,3 }) << endl;
	return 0;
}

练习6.28

string类型

练习6.29

可以声明,也可以不声明.

练习6.30

bool str_subrange(const string& str1, const string& str2)
{
	if (str1.size() == str2.size())
		return str1 == str2;
	auto size = (str1.size() < str2.size()) ? str1.size() : str2.size();
	for (decltype(size) i = 0; i != size; ++i)
		if (str1[i] != str2[i])
			return;
}

报错: 函数必须返回值.