C++ [进制转换]十六进制转化为二进制

C++ [进制转换]十六进制转化为二进制

思路：利用输入十六进制字符串，然后从前往后逐一提取单一字符，转换为整形变量，在应用 switch-case 来对应到此数对应的二进制四位上。

注意：字符转换为整形变量时应该考虑 ASCII 码上的位置转化、输出时的二进制的四位应当用引号引起来。

#include<iostream>
#include<cctype>
using namespace std;
int main()
{
	int f,c;
	char e;
	string hexDigit;
	cin>>hexDigit;
	for(int f=0;f<=hexDigit.length();f++)
	{
		e=hexDigit[f];
		if(e>='A'&&e<='F')
		{
			int a=static_cast<int>(e-'A'+10);
			switch(a)
			{
				case 10:cout<<"1010";break;
				case 11:cout<<"1011";break;
				case 12:cout<<"1100";break;
				case 13:cout<<"1101";break;
				case 14:cout<<"1110";break;
				case 15:cout<<"1111";break;
			}
		}
		else if(isdigit(e))
		{
			int b=static_cast<int>(e-'0');
			switch(b)
			{
				case 1:cout<<"0001";break;
				case 2:cout<<"0010";break;
				case 3:cout<<"0011";break;
				case 4:cout<<"0100";break;
				case 5:cout<<"0101";break;
				case 6:cout<<"0110";break;
				case 7:cout<<"0111";break;
				case 8:cout<<"1000";break;
				case 9:cout<<"1001";break;
			}
		}
	}
	return 0;
}

去除前导0:

#include <iostream>
#include<cctype>

using namespace std;

int main() {
    string hexDigit, binaryDigit;
    cin >> hexDigit;
    for (int i = 0; i < hexDigit.length(); ++i) {
        char e = hexDigit[i];
        if (e >= 'A' && e <= 'F') {
            int a = static_cast<int>(e - 'A' + 10);
            switch (a) {
                case 10:
                    binaryDigit += "1010";
                    break;
                case 11:
                    binaryDigit += "1011";
                    break;
                case 12:
                    binaryDigit += "1100";
                    break;
                case 13:
                    binaryDigit += "1101";
                    break;
                case 14:
                    binaryDigit += "1110";
                    break;
                case 15:
                    binaryDigit += "1111";
                    break;
            }
        } else if (isdigit(e)) {
            int b = static_cast<int>(e - '0');
            switch (b) {
                case 1:
                    binaryDigit += "0001";
                    break;
                case 2:
                    binaryDigit += "0010";
                    break;
                case 3:
                    binaryDigit += "0011";
                    break;
                case 4:
                    binaryDigit += "0100";
                    break;
                case 5:
                    binaryDigit += "0101";
                    break;
                case 6:
                    binaryDigit += "0110";
                    break;
                case 7:
                    binaryDigit += "0111";
                    break;
                case 8:
                    binaryDigit += "1000";
                    break;
                case 9:
                    binaryDigit += "1001";
                    break;
            }
        }
    }
    bool flag = false;
    for (int j = 0; j < binaryDigit.length(); ++j) {
        if (binaryDigit[j] == '1'|| flag) {
            flag = true;
            cout << binaryDigit[j];
        }
    }
    return 0;
}