程序代码：

#include <stdio.h>
#include <limits.h>

unsigned character_offset( unsigned bit_number )
{

    int c1=bit_number / CHAR_BIT;
    return c1;                       //计算bit_number第几个字节内
}

unsigned bit_offset( unsigned bit_number )
{
    int j=bit_number % CHAR_BIT;
    return j;                       //计算bit_number 在最高字节里是第几位
}

void set_bit( char bit_array[], unsigned bit_number )    //把指定的位设置为 1
{
    printf("char %c\n",bit_array[character_offset(bit_number)]);
    printf("int  %d\n",bit_array[character_offset(bit_number)]);

    bit_array[ character_offset(bit_number) ] |=
    ( 1 << bit_offset(bit_number) );

    printf("char %c\n",bit_array[character_offset(bit_number)]);
    printf("int  %d\n",bit_array[character_offset(bit_number)]);
}

int main()
{
    char a[20] = "10001100001";
    printf("int       a[0]=%d\nchar      a[0]=%c\n",a[0],a[0]);
    printf("CHAR_BIT: %d\n",CHAR_BIT);
    set_bit(a, 10);
    printf( "%s\n",a );

    return 0;
}