C++将10进制字符串转为16进制字符串

方法一：

推荐 直接除以16进行计算 对结果递归进行转换运算

代码如下：

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

string DecIntToHexStr(long long num)
{
	string str;
	long long Temp = num / 16;
	int left = num % 16;
	if (Temp > 0)
		str += DecIntToHexStr(Temp);
	if (left < 10)
		str += (left + '0');
	else
		str += ('A' + left - 10);
	return str;
}

string DecStrToHexStr(string str)
{
	long long Dec = 0;
	for (int i = 0; i < str.size(); ++i)
		Dec = Dec * 10 + str[i] - '0';
	return DecIntToHexStr(Dec);
}
int main()
{
	string DecStr;
	while (cin >> DecStr)
	{
		cout << "0x" + DecStrToHexStr(DecStr);
	}
	return 0;
}

方法二：先十进制转为二进制，然后再每四位进行合并转为16进制

代码如下：

#include<iostream>
#include <string>
#include<vector>
#include <sstream>
#include <math.h>
using namespace std;

int main()
{
	string decStr;
	cin >> decStr;
	int num = stoi(decStr);
	vector<int>v;
	while (num)
	{
		int bit = num % 2;
		v.push_back(bit);
		num = num / 2;
	}
	reverse(v.begin(), v.end());
	string hexStr;
	if (v.size() % 4 == 0)
	{
		for (int i = 0; i < v.size() / 4; ++i)
		{
			int temp = 0, k = 3;
			for (int j = i * 4; j < (i + 1) * 4; ++j)
			{
				if (v[j] == 1)
					temp += pow(2, k);
				--k;
			}
			if (temp <= 9)
				hexStr += temp;
			else
				hexStr += ('A' + temp - 10);
		}
	}
	else
	{
		int zeroNum = 4 - v.size() % 4;
		for (int i = 0; i < zeroNum; ++i)
			v.insert(v.begin(), 0);
		for (int i = 0; i < v.size() / 4; ++i)
		{
			int temp = 0, k = 3;
			for (int j = i * 4; j < (i + 1) * 4; ++j)
			{
				if (v[j] == 1)
					temp += pow(2, k);
				--k;
			}
			if (temp <= 9)
			{
				stringstream ss;
				string strTemp;
				ss << temp;
				ss >> strTemp;
				hexStr += strTemp;
			}
			else
				hexStr += ('A' + temp - 10);
		}
	}
	cout << hexStr << endl;
	return 0;
}