用getchar输入，打印的二进制为什么会多2个1

寻觅者6

小弟写了一个把输入的字符型整数转化成二进制显示的程序，不知什么问题，用getchar得到的总是多2个1。望请大神们前来指出错误来。
#include<stdio.h>
#include<stdlib.h>

int print_2b(char a)
{
   unsigned char b = 0x80;

   while( b > 0)
   {
      putchar(a & b ? '1' : '0' );
      b >>=1;
   }
      puts("\n";
}
int main()
{
     print_2b(getchar());
    return 0;
}
file:///C:/Users/lenovo/AppData/Local/YNote/data/qqEC40F61F6498141C01FB27C32DDB73C7/6e95442ee9494c5f9c491b57916876d6/4d46840cdede487dadcf5f3d229efb17.jpg
file:///C:/Users/lenovo/AppData/Local/YNote/data/qqEC40F61F6498141C01FB27C32DDB73C7/6e95442ee9494c5f9c491b57916876d6/4d46840cdede487dadcf5f3d229efb17.jpgfile:///C:/Users/lenovo/AppData/Local/YNote/data/qqEC40F61F6498141C01FB27C32DDB73C7/6e95442ee9494c5f9c491b57916876d6/4d46840cdede487dadcf5f3d229efb17.jpgfile:///C:/Users/lenovo/AppData/Local/YNote/data/qqEC40F61F6498141C01FB27C32DDB73C7/6e95442ee9494c5f9c491b57916876d6/4d46840cdede487dadcf5f3d229efb17.jpg

hellioncu

因为getchar得到的1实际是字符1，ascii码是0x31