[C++]进制转换(2~16)

版权声明：Copyright © 2018-2018 Takaway 复习用，转载注明一下就行了~ https://blog.csdn.net/LynlinBoy/article/details/83904744

Tips：此Code引用了STL库，已引用函数注释如下：

Origin Url：http://www.cplusplus.com/reference/algorithm/reverse/

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template <class BidirectionalIterator>
void reverse (BidirectionalIterator first, BidirectionalIterator last);

反向范围 

反转范围中元素的顺序[first,last)。
函数调用iter_swap将元素交换到新位置。
此函数模板的行为等效于：

template <class BidirectionalIterator>
void reverse (BidirectionalIterator first, BidirectionalIterator last) {
    while ((first != last) && (first != --last)) {
        std::iter_swap (first, last);
        ++first;
    };
};

参数 first, last

双向迭代器到要反转的序列的初始和最终位置。使用的范围是[first,last)，它包含所有的元件第一和最后一个，包括由指向的元件第一但不被指向的元素最后。
BidirectionalIterator 应指向哪种类型 交换 是否正确定义。 

例子

// reverse algorithm example
#include <iostream>     // std::cout
#include <algorithm>    // std::reverse
#include <vector>       // std::vector

int main () {
  std::vector<int> myvector;

  // set some values:
  for (int i=1; i<10; ++i) myvector.push_back(i);   // 1 2 3 4 5 6 7 8 9

  std::reverse(myvector.begin(),myvector.end());    // 9 8 7 6 5 4 3 2 1

  // print out content:
  std::cout << "myvector contains:";
  for (std::vector<int>::iterator it=myvector.begin(); it!=myvector.end(); ++it)
    std::cout << ' ' << *it;
  std::cout << '\n';

  return 0;
}

输出：myvector contains: 9 8 7 6 5 4 3 2 1

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程序代码：

#include <algorithm>
#include <iostream>
#include <string>
#include <cstdio>
#include <cctype>
using namespace std;
const char Form[] = {"0123456789ABCDEF"};
inline int data(const char ch) {
	for (int i = 0; i < 16; ++i)
		if (ch == Form[i])
			return i;  
	return -1;	
};
inline void a_to_decimal(const int a, string &str) {
	const int len = str.length();
	int answer = 0; int weight = 1;
	for (int i = len - 1; i >= 0; --i) {
		int temp = data(str[i]);
		answer += temp * weight;
		weight *= a;	
	};
	string cache = "";
	while (answer > 0) {
		cache.push_back(answer % 10 + '0');
		answer /= 10;	
	};
	reverse(cache.begin(), cache.end());
	str = cache;
};
inline void decimal_to_b(const int b, string &str) {
	const int len = str.length();
	int answer = 0; int weight = 1;
	for (int i = len - 1; i >= 0; --i) {
		int temp = data(str[i]);
		answer += temp * weight;
		weight *= 10;	
	};
	string cache = "";
	while (answer > 0) {
		cache.push_back(Form[answer % b]);
		answer /= b;	
	};
	reverse(cache.begin(), cache.end());
	str = cache;
};
inline void conversion(const int a, string &str, const int b) {
	a_to_decimal(a, str);
	decimal_to_b(b, str);
	
	if (str.empty()) str.push_back('0');	
};
int main(int argc, char *argv[]) {
	int a, b; string str; cin >> a >> str >> b;
	for (int i = 0; i < str.size(); ++i) str[i] = toupper(str[i]);
	conversion(a, str, b);
	cout << str << endl; 
	return 0;	
};

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