题解 | #10进制 VS 2进制#

难点在于实现模拟人手动计算加法和乘法的过程
#include<vector>
#include<string>
#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;

string Divde(string str, int x) {
	int remainder = 0;
	for (int i = 0; i < str.size(); i++) {
		int temp = remainder * 10 + str[i] - '0';
		str[i] = temp / x +'0';
		remainder = temp % 2;

	}
	int pos = 0;
	while (str[pos++] == '0');
	pos--;
	str = str.substr(pos);
	return str;
}

string Multiple(string str,int x) { //实现字符串的乘法
	int carry = 0; // 保存进位
	for (int i = str.size() - 1; i >= 0; i--) {
		int current = x * (str[i] - '0') + carry;
		str[i] = current % 10 + '0';
		carry = current / 10;

	}
	if (carry != 0)
		str = "1" + str;
	return str;
}

string Add(string str, int x) {  //实现字符串的加法
	int carry = x;//记录进位
	for (int i = str.size() - 1; i >= 0; i--) {
		int temp = (str[i]-'0') + carry;
		str[i] = temp % 10+'0';
		carry = temp / 10;
	}
	if (carry != 0)
		str = "1" + str;
	return str;


}



int main() {
	string  str;
	while (cin >> str) {
		vector<int> vec;
		while (str != "") {
			vec.push_back((str[str.size()-1 ]-'0') % 2);
			str = Divde(str, 2);
		}
		//此时得到便为二进制的逆序
		string answer = "0";
		for (int i =0; i < vec.size(); i++) {
			answer = Multiple(answer, 2);
			answer = Add(answer, vec[i]);

		}
		cout << answer << endl;
	}
}