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