朝阳区龙文学校:帮忙看看哪错了？

我编了个程序，关于8 10 16进制换算的，如下：
main()
{
long x;
char i,a,b,c;
i=020;
printf ("10%ca\n",i);
printf (" 8%cb\n",i);
printf ("16%cc\n",i);
if (getchar ()=='a')
{
printf ("To 8,Press m\n");
printf ("To 16,Press n\n");
if(getchar ()=='m')
{
printf ("Please give me your number\n");
scanf ("%d",&x);
printf ("%o",x);
}
else if(getchar ()=='n')
{
printf ("Please give me your number\n");
scanf ("%d",&x);
printf ("%x",x);
}
else
printf ("error\n");
}
else if (getchar ()=='b')
{
printf ("To 10,Press m\n");
printf ("To 16,Press n\n");
if (getchar ()=='m')
{
printf ("Please give me your number\n");
scanf ("%o",&x);
printf ("%d",x);
}
else if (getchar ()=='n')
{
printf ("Please give me your number\n");
scanf ("%o",&x);
printf ("%x",x);
}
else
printf ("error\n");
}
else if (getchar ()=='c')
{
printf ("To 10,Press m\n");
printf ("To 16,Press n\n");
if (getchar ()=='m')
{
printf ("Please give me your number\n");
scanf ("%x",&x);
printf ("%d",x);
}
if (getchar ()=='n')
{
printf ("Please give me your number\n");
scanf ("%x",&x);
printf ("%o",x);
}
else
printf ("error\n");
}
else
printf ("error\n");

}
帮忙看一下哪错了？
怎么不好用？
谢了