用另外一种思路给你写了段代码，这个效率应该比前面那个逐位判断的方法要快很多！

#include<stdio.h>

typedef  unsigned char BYTE;
typedef struct  //bit型位结构体       
{
    unsigned char bit0:1;
    unsigned char bit1:1;
    unsigned char bit2:1;
    unsigned char bit3:1;
    unsigned char bit4:1;
    unsigned char bit5:1;
    unsigned char bit6:1;
    unsigned char bit7:1;
}bit_array;    

/*............显示传入参数的二进制形式.........*/

void byte_change(BYTE* str, unsigned int len)   
{
    BYTE i=0;
    bit_array *temp=NULL;
    temp=(bit_array *)str;   //强制转换类型
    while(i<len)
    {
        printf("%d%d%d%d%d%d%d%d ", (temp+i)->bit7,  (temp+i)->bit6,
                        (temp+i)->bit5,  (temp+i)->bit4,
                        (temp+i)->bit3,  (temp+i)->bit2,
                        (temp+i)->bit1,  (temp+i)->bit0);
        i++;
    }
}
int main(void)
{
    BYTE array[]={8,7,6,5,4,3,2,1};    //代转换的数组
    byte_change(array,sizeof(array)/sizeof(array[0]));
    printf("\n");
    return 0;
}

谢谢你的帮助！

[[it] 本帖最后由 s_lujun 于 2008-8-13 17:49 编辑 [/it]]

#include <stdio.h>
#include <limits.h>
#include <string.h>
#define MAX_SIZE  256
typedef char byte ;
void DisplayBin(byte  * ptr ) {
                unsigned int len = strlen(ptr) ;
                unsigned int  i = 0 ;
                unsigned short mask = 0x0 ;
                while(i<= len )
                      ptr[i] = ptr[i++] - '0' ;
                i = 0 ;
                while(i < len) {
                      mask = 0x1 << CHAR_BIT - 1 ;
                      while(mask){
                            putchar((mask & *ptr)?'1':'0') ;
                            mask >>= 0x1 ;

                      }
                      i++ ;
                      ptr++ ;
                      putchar(' ') ;
                }
                putchar('\n') ;
 return  ;
}

int main(void) {
         byte  arr[MAX_SIZE] ;
         scanf("%[0-9]s" ,arr) ;
         DisplayBin(arr) ;
 return 0 ;
 }