c++ 进制转换由十六进制转换成二进制

void change16_2()
{
printf("十六进制->二进制\n");
int i,a,b,c,d,k;
int x[3];
char m[3]={0,0,0},n[3];
printf("转换数（十六进制）：");
scanf("%s",m);

for(i=0;i {
if(m[i]>='A'&&m[i]<='F')
{
x[i]=10+m[i]-65;
printf("%d\n",x[i]);
}
else
{
if(m[i]>='0'&&m[i]<='9')
{
x[i]=m[i]-48;
printf("%d\n",x[i]);
}
else
{
printf("输入错误！\n");
}
}
}
for(i=0;i<3;i++)
{
printf("%d=%c\n",i,x[i]);
}
for(a=0;a<=1;a++)
{
for(b=0;b<=1;b++)
{
for(c=0;c<=1;c++)
{
for(d=0;d<=1;d++)
{
if(m[0]==8*a+4*b+2*c+d)
{
printf("a=%d\n",a);
printf("b=%d\n",b);
printf("c=%d\n",c);
printf("d=%d\n\n",d);
n[2]=a*1000+b*100+c*10+d;
}
if(m[1]==8*a+4*b+2*c+d)
{
printf("a=%d\n",a);
printf("b=%d\n",b);
printf("c=%d\n",c);
printf("d=%d\n",d);
n[1]=a*1000+b*100+c*10+d;
}
if(m[2]==8*a+4*b+2*c+d)
{
printf("a=%d\n",a);
printf("b=%d\n",b);
printf("c=%d\n",c);
printf("d=%d\n",d);
n[2]=a*1000+b*100+c*10+d;
}
}
}
}
}
k=n[0]*100000000+n[1]*10000+n[2];
printf("k=%d\n",k);
printf("转化为（二进制）：");
for(i=0;i<3;i++)
{
printf("%c",n[i]);
}
printf("\n\n");
}
进制转换怎么不对，如果m字符串 输入A 就会输出两次“输入错误”，这是为什么，这里的输入要怎么改

16进制转2进制需要那么复杂么？直接查表就可以了。每个16进制字符对应4个二进制字符

 void printhextobin(char c)
{
    char x[17][5] = {
        "0000", "0001", "0010", "0011",
        "0100", "0101", "0110", "0111",
        "1000", "1001", "1010", "1011",
        "1100", "1101", "1110", "1111", "xxxx"
    };
    int n = 16;
    if (c >= 'a' && c <= 'f') n = c - 'a' + 10;
    if (c >= 'A' && c <= 'F') n = c - 'A' + 10;
    if (c >= '0' && c <= '9') n = c - '0';
    printf("%s", x[n]);
}
int main()
{
    char c[] = "abc123";
    for (int i = 0; i < 6; i++) printhextobin(c[i]);
}

101010111100000100100011