第 15 章 位操作（invert4）

 /*------------------------------------

     invert4.c -- 使用位操作显示二进制

 ------------------------------------*/

 #include <stdio.h>

 #include <limits.h>        //提供 CHAR_BIT 的定义，CHAR_BIT 表示每字节的位数

 char* itobs(int, char*);

 void show_bstr(const char*);

 int invert_end(int num, int bits);

 int main()

 {

     char bin_str[CHAR_BIT * sizeof(int) + ];

     int number;

     puts("Enter integers and see them in binary.");

     puts("Non-numeric input terminates program");

     while (scanf("%d", &number) == )

     {

         itobs(number, bin_str);

         printf("%d is ", number);

         show_bstr(bin_str);

         putchar('\n');

         number = invert_end(number, );

         printf("Inverting the last 4 bits gives\n");

         show_bstr(itobs(number, bin_str));

         putchar('\n');

     }

     puts("Bye");

     return ;

 }

 char* itobs(int n, char *ps)

 {

     const static int size = CHAR_BIT * sizeof(int);

     for (int i(size - ); i >= ; --i, n >>= )

         ps[i] = ( & n) + '';

     ps[size] = '\0';

     return ps;

 }

 //以4位为一组，显示二进制字符串

 void show_bstr(const char *str)

 {

     int i = ;

     while (str[i])        //不是空字符

     {

         fputc(str[i], stdout);

         if (++i %  ==  && str[i])

             fputc(' ', stdout);

     }

 }

 int invert_end(int num, int bits)

 {

     int mask = ;

     int bitval = ;

     while (bits-- > )

     {

         mask |= bitval;

         bitval <<= ;

     }

     return num ^ mask;

 }

invert4.c