5.4的习题：编写一组函数，实现维数组，函数原型如下：
//指定位设置为1
void set_bit(char bit_array[], unsigned bit_number); //指定位清零
void clear_bit(char bit_array[], unsigned bit_number);
//指定位清零，否则设置为1
void assign_bit(char bit_array[], unsigned bit_number， int value); //参数指定位置为1返回真，为0返回1
int test_bit(char bit_array[], unsigned bit_number);
每个函数第一位是字符数组，实际存储所有的位，第二位参数用于标示，要访问的位，函数的调用者要防止这个值过大，超过数组边界。
//字符偏移
unsigned int char_offset(unsigned bit_number)
{
return bit_number / CHAR_BIT;
} //bit位偏移
unsigned int bit_offset(unsigned bit_number)
{
return bit_number % CHAR_BIT;
} void set_bit(char bit_array[], unsigned bit_number)
{
bit_array[char_offset(bit_number)] |= 1 << bit_offset(bit_number);
} void clear_bit(char bit_array[], unsigned bit_number)
{
bit_array[char_offset(bit_number)] &= ~(1 << bit_offset(bit_number));
} void assign_bit(char bit_array[], unsigned bit_number, int value)
{
if (value != 0) {
set_bit(bit_array, bit_number);
}
else {
clear_bit(bit_array, bit_number);
}
} int test_bit(char bit_array[], unsigned bit_number)
{
//对该bit位进行与操作，如果是1则结果还是 1<< (bit_number % CHAR_BIT)
unsigned isZero = bit_array[bit_number / CHAR_BIT] & (1 << (bit_number % CHAR_BIT));
if (isZero == (1 << (bit_number % CHAR_BIT))) {
return TRUE;
}
return FALSE;
}