C语言，进制转换之二进制转十六进制，完整代码

#include "iostream"
using namespace std;
#define MAX 50
int _2to16()//二转十六
{
cout << "请输入二进制数，并以‘$’结束：";
char elem2[MAX];
int flag = 1;
char ch;
int i = 0;
while (flag)
{
cin >> ch;
if (ch != '$')
{
elem2[i] = ch;
i++;
}
else
{
flag = 0;
}
}
int length = i;
int n = 0;
int sum = 0;
int product = 0;
if (length % 4 != 0)//将缺位的二进制码用0补齐
{
int n = 4 - length % 4;
int i = 0;
for (i = length - 1; i >= 0; i--)
elem2[i + n] = elem2[i];
length += n;
for (i = 0; i < n; i++)
elem2[i] = '0';
cout << "补齐之后的内容是：" << endl;
for (i = 0; i < length; i++)
cout << elem2[i]<<" ";
cout << endl;
}
for (n = 0; n < length; n++)//判断是否是二进制数
{
if ('1' == elem2
|| '0' == elem2
)
sum++;
}
if (sum == length)
{
char elem16[MAX];
int r = 0;
int m = 0;
int p = 0;
int q = 0;
for (m = length - 1; m >= 0; m--)
{
q = elem2[m] - '0';
product += q * pow(2, p);
p++;
if (4 == p)
{
if (product>9)
elem16[r] = product+55;//输出A...F范围
else
{
elem16[r] = product+48;//输出0...9范围
}
r++;
p = 0;
product = 0;
}
}
int j = 0;
cout << "对应的十六进制数是：OX";
for (j = r - 1; j >= 0; j--)
cout << elem16[j];
cout << endl;

}
else
{
cout << "你输入的不是二进制数！" << endl;
}
return 0;
}