essential c++第二章课后练习题

练习2.2

#include <vector>
#include <iostream>

const std::vector<int>* penta_seq(int size) {
	const int max_size = 1024;
	static std::vector<int>elems;
	if (size <= 0 || size > max_size) {
		std::cerr << "the size is illeage"
			<< size << "can't fulfill request" << std::endl;
		return 0;
	}
	for (int ix = 0; ix <size;++ix)
	{
		int seq_num = (ix*(3 * ix - 1)) / 2;
		elems.push_back(seq_num);		
		}		
	return &elems;
	}

void display() {
	int a;
	std::cout << "enter the size number";
	std::cin >> a;
	const std::vector<int> elems = *penta_seq(a);
	//it is a point now
	std::cout << "now the pentagonal seq is ";
	for (auto it = elems.begin(); it != elems.end(); ++it) {
		std::cout << *it<<" " ;
	}
	std::cout << std::endl;
}

int main() {
	display();
	getchar();

}

练习2.3

#include <iostream>

inline bool is_size_ok(int size) {
	const int max_size = 1024;
	if (size <= 0 || size > max_size)
		return false;
	else
		return true;	
}

const std::vector<int>* penta_seq(int size) {
	
	static std::vector<int>elems;
	if (!is_size_ok) {
		return 0;
	}
	for (int ix = 0; ix <size;++ix)
	{
		int seq_num = (ix*(3 * ix - 1)) / 2;
		elems.push_back(seq_num);		
		}		
	return &elems;
	}

void display() {
	int a;
	std::cout << "enter the size number";
	std::cin >> a;
	const std::vector<int> elems = *penta_seq(a);
	//it is a point now
	std::cout << "now the pentagonal seq is ";
	for (auto it = elems.begin(); it != elems.end(); ++it) {
		std::cout << *it<<" " ;
	}
	std::cout << std::endl;
}

int main() {
	display();
	system("pause");
}

练习2.4
同上2.2，略

练习2.5，练习2.6

#include <vector>
#include <iostream>
#include <string>
#include <algorithm>

template<typename T>
T load_max(T a, T b) {
	T c =(a>b)?a:b ;
	return c;
}


int main() {
	std::string a = "asdsa";
	std::string b = "qwefs";
	std::cout<<load_max(a, b);
	getchar();
	
}

补充lambda表达式，python中也有，但C++中的与template联用有独特用法。

int main() {
	int a=1; int b=2;
	//lambda表达式
	auto c = [a,b](int d) {
		return a + b + d;
	};
	std::cout << c(12);
	getchar();
}