C++primer 习题第四章（1）

4.7编写代码实现一个数组赋值给另外一个数组，然后将这段代码改用vector实现。考虑如何将一个vector 赋值给另一个vector。

int main()
{
	int a[3] = { 1,2,3 };
	int b[3];
	cout << "array :" << endl;
	for (int i = 0; i < 3; i++)
	{
		b[i] = a[i];
		cout << b[i] << endl;
	}
	

	vector<int> ivec1 = { 1, 2, 3 };
	cout << "ivec1:" << endl;
	for (vector<int>::iterator iter = ivec1.begin(); iter != ivec1.end(); ++iter)
	{
		cout <<*iter<< endl;
	}
	
	vector<int>ivec2(ivec1);
	vector<int> vec;
	vec = ivec2;
	cout << "ivec2:" << endl;
	for (vector<int>::iterator iter = ivec2.begin(); iter != ivec2.end(); ++iter)
	{
		cout << *iter << endl;
	}
	cout << "vec:" << endl;
	for (vector<int>::iterator iter = vec.begin(); iter != vec.end(); ++iter)
	{
		cout << *iter << endl;
	}
	return 0;

}

4.8 编写程序判断两个数组是否相等，然后编写一段类似的程序比较两个vector。

int main()
{
	int a[3] = { 1, 2, 3 };
	int b[3] = { 1, 2, 3 };
	cout << "use array:" << endl;
	if (sizeof(a) / sizeof(int) == sizeof(b) / sizeof(int))
	{
		size_t i = 0;
		for (i; i < sizeof(a) / sizeof(int); ++i)
		{
			if (a[i] != b[i])
			{
				cout << "两数组不相等" << endl;
				break;
			}
		}
		if (sizeof(a) / sizeof(int) == i)
		{
			cout << "两数组相等" << endl;
		}
	}
	cout << "use vector :" << endl;
	vector<int> vec = { 1, 2, 3, 4 };
	vector<int> vec2 = { 1, 2, 3, 4 };
		if (vec == vec2){
			cout << "两数组相等" << endl;
		}
		else
			cout << "两数组不相等" << endl;
	return 0;

}

4.9 编写程序定义一个有10个int型元素的数组，并以其在数组中的位置作为各元素的初值。

int main()
{
	int a[10];
	for (int i = 0; i < 10; ++i){
		a[i] = i;
		cout << a[i] << endl;
	}
	
	cout << "use vector" << endl;
	vector<int> vec;
	for (int i = 0; i < 10; ++i){
		vec.push_back(i);
	}
	for (vector<int>::iterator iter = vec.begin(); iter != vec.end(); ++iter){
		cout << *iter << endl;
	}

	return 0;

}

4.14 编写代码修改指针的值，然后在编写代码修改指针所指对象的值。

int main()
{
	int a (1),c(2);

	int *b = &a;
	b = &c;
	*b = 6;
	return 0;

}

4.16 下列程序实现什么功能？

int main()
{
	int i = 42, j = 1024;
	int *p1 = &i, *p2 = &j;
	*p2 = *p1 * *p2;
	*p1 *= *p1;
	cout << *p1 << "   "<<*p2 << endl;
	return 0;

}

4.18 编写一个程序，使用指针把一个int型数组的所有元素设置成0。

int main()
{
	int  a[3] = { 1, 2, 3 };
	
	for (int *p = a; p != a + 3; ++p){
		*p = 0;
	}
	for (int i = 0; i < 3; ++i){
		cout << a[i] << endl;
	}

}

4.25 编写程序比较两个string字符串，然后编写程序比较两个C风格字符串。

int main()
{
	cout << "C++ style!" << endl;
	string str1 = "hello world";
	string str2 = "good well";
	if (str1 == str2){
		cout << "两字符串相等" << endl;
	}
	else
		cout << "两字符串不相等" << endl;

	cout << "C style!" << endl;
	char ch1[] = "hello world";
	char ch2[] = "good well";
	if (!strcmp(ch1, ch2)){
		cout << "两字符串相等" << endl;
	}
	else
		cout << "两字符串不相等" << endl;

}