复习题1、将下列十进制数转换为二进制形式：
a. 3
b. 13
c. 59
d. 119
答：
a. 11
b. 1101
c. 111011
d. 1110111
2、将下列二进制值转换为十进制、八进制和十六进制形式：
a. 00010101
b. 01010101
c. 01001100
d. 10011101
答：
a. 21, 025, 0x15
b. 85, 0125, 0x55
c. 76, 0114, 0x4C
d. 157, 0235, 0x9D
3、计算下列表达式；假设每个值为8位：
a. ~ 3
b. 3 & 6
c. 3 | 6
d. 1 | 6
e. 3 ^ 6
f. 7 >> 1
g. 7 << 2
答：
a. 252
d. 2
c. 7
d. 7
e. 5
f. 3
g. 28
4、计算下列表达式；假设每个值为8位：
a. ~ 0
b. !0
c. 2 & 4
d. 2 && 4
e. 2 | 4
f.2 || 4
g. 5 << 3
答：
a. 255
b. 1
c. 0
d. 1
e. 6
f. 1
g. 40
5、因为ASCII码仅使用最后的7位，所以有时需要屏蔽掉其他位。相应的二进制掩码是什么？分别以十进制、八进制和十六进制形式如何表示这个掩码？
答：掩码在二进制中为1111111。它的十进制表示为127，八进制表示为0177，十六进制表示为0x7F。
6、在程序清单15.2中，可以做以下替换，把：
while(bits-- > 0)
{
mask |= bitval;
bitval <<= 1;
}
用：
while(bits-- > 0)
{
mask |= bitval;
bitval *= 2;
}
替换，而程序仍将工作。这是否意味着*= 2等同于<<= 1？|=和+=又怎样？
答：
bitval *= 2和bitval << 1都把bitval的当前值加倍，所以他们是等效的。但是mask += bitval和mask |= bitval只有在bitval和mask没有同时设置为打开的位时才具有相同的效果。例如，2 | 4 = 6，但是3 | 6 = 7。
7、
a. Tinkerbell计算机有一个硬件字节，可以将该字节读入程序。该字节包括下列信息：
| 位 | 含义 |
| 0到1 | 1.4MB软盘驱动器数量 |
| 2 | 未使用 |
| 3到4 | CD-ROM驱动器数量 |
| 5 | 未使用 |
| 6到7 | 硬盘驱动器数量 |
Tinkerbell和IBM PC一样从右到左填充结构位字段。创建一个适于存放该信息的位字段模板。
b. Klinkerbell与Tinkerbell类似，但它从左到右填充结构。请为Klinkerbell创建相应的位字段模板。
答：
a.
struct tinkerbell {
unsigned int diskdrivers : 2;
unsigned int : 1;
unsigned int cdromdrivers: 2;
unsigned int : 1;
unsigned int harddrivers : 2;
};
b.
struct klinkerbell {
unsigned int harddrivers : 2;
unsigned int : 1;
unsigned int cdromdrivers: 2;
unsigned int : 1;
unsigned int diskdrivers : 2;
};
编程练习1、
#include <stdio.h>
#include <string.h>
#include <math.h>
int stoi(char *);
int main(void)
{
char pbin[9];
printf("请输入一个(8位)二进制字符串：\n");
puts("在一行开始处键入[Enter]结束循环：");
while(fgets(pbin, 9, stdin) != NULL && pbin[0] != '\n')
{
printf("二进制序列%s转换为十进制数为: %d\n", pbin, stoi(pbin));
while(getchar() != '\n')
continue;
printf("请输入一个二进制字符串：\n");
}
printf("Bye!\n");
return 0;
}
int stoi(char * s)
{
int len = strlen(s);
unsigned int tot = 0;
for(int i = 0; i < len; i++)
if(s[i] == '1')
tot += pow(2, len - 1 - i);
return tot;
}
看看别人写的代码（借鉴h
ttp://ptgmedia.pearsoncmg.com/images/9780321928429/downloads/9780321928429_ProgrammingExerciseAnswers_Selected.pdf）
即优美又考虑周全，要学习！！！
#include <stdio.h>
#include <stdbool.h>
#include <limits.h> // for CHAR_BIT 一个char的位数
#include <string.h>
int bstr_to_dec(const char * str);
bool check_val(const char * str);
char * s_gets(char * st, int n);
int main(void)
{
const size_t SLEN = CHAR_BIT * sizeof(int) + 1;
char value[SLEN];
printf("Enter a binary number with up to %zu digits: ", SLEN - 1);
while(s_gets(value, SLEN) != NULL && value[0] != '\0')
{
if(!check_val(value))
puts("A binary number contains just 0s and 1s.");
else
printf("%s is %d\n", value, bstr_to_dec(value));
puts("Enter next number (empty line to quit): ");
}
puts("Done");
return 0;
}
bool check_val(const char * str)
{
bool valid = true;
while(valid && *str != '\0')
{
if(*str != '0' && *str != '1')
valid = false;
str++;
}
return valid;
}
int bstr_to_dec(const char * str)
{
int val = 0;
while(*str != '\0')
val = 2 * val + (*str++ - '0'); // 二进制——>十进制太神奇了
return val;
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if(ret_val)
{
find = strchr(ret_val, '\n');
if(find)
*find = '\0';
else
while(getchar() != '\n')
continue;
}
return ret_val;
}
2、
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <limits.h> // for CHAR_BIT 一个char的位数
#include <string.h>
int bstr_to_dec(const char * str);
char * itobs(int n, char * ps);
void show_bstr(const char * str);
int main(int argc, char *argv[])
{
const size_t SLEN = CHAR_BIT * sizeof(int) + 1;
char bin_str[SLEN];
int value0, value1, value3;
if(argc != 3)
{
printf("输入格式错误!\n");
printf("请按照\"%s 字符串 字符串\"格式输入\n");
exit(1);
}
value0 = bstr_to_dec(argv[1]);
value1 = bstr_to_dec(argv[2]);
printf("~%s = ", argv[1]);
show_bstr(itobs(~value0, bin_str));
printf("\n~%s = ", argv[2]);
show_bstr(itobs(~value1, bin_str));
value3 = value0 & value1;
printf("\n%s & %s = ", argv[1], argv[2]);
show_bstr(itobs(value3, bin_str));
value3 = value0 | value1;
printf("\n%s | %s = ", argv[1], argv[2]);
show_bstr(itobs(value3, bin_str));
value3 = value0 ^ value1;
printf("\n%s ^ %s = ", argv[1], argv[2]);
show_bstr(itobs(value3, bin_str));
return 0;
}
int bstr_to_dec(const char * str)
{
int val = 0;
while(*str != '\0')
val = 2 * val + (*str++ - '0'); // 二进制——>十进制太神奇了
return val;
}
char * itobs(int n, char * ps)
{
int i;
static int size = CHAR_BIT * sizeof(int);
for(i = size - 1; i >= 0; i--, n >>= 1)
ps[i] = (01 & n) + '0';
ps[size] = '\0';
return ps;
}
/* 4位一组显示二进制字符串 */
void show_bstr(const char * str)
{
int i = 0;
while(str[i])
{
putchar(str[i]);
if(++i % 4 == 0 && str[i])
putchar(' ');
}
}
运行结果图：
3、
#include <stdio.h>
#include <limits.h> // for CHAR_BIT 一个char的位数
char * itobs(int n, char * ps);
int get_count(const char *);
int main(void)
{
const size_t SLEN = CHAR_BIT * sizeof(int) + 1;
char bin_str[SLEN];
int number, count;
puts("请输入一个整数: ");
while(scanf("%d", &number) == 1)
{
count = get_count(itobs(number, bin_str));
printf("%d这个数中打开的位的数量: %d\n", number, count);
puts("请输入一个整数: ");
}
puts("Bye!");
return 0;
}
char * itobs(int n, char * ps)
{
int i;
static int size = CHAR_BIT * sizeof(int);
for(i = size - 1; i >= 0; i--, n >>= 1)
ps[i] = (01 & n) + '0';
ps[size] = '\0';
return ps;
}
int get_count(const char * ps)
{
int count = 0;
while(*ps != '\0')
if(*ps++ == '1')
count++;
return count;
}
4、
#include <stdio.h>
#include <limits.h> // for CHAR_BIT 一个char的位数
int fun_itobs(int n, int index);
int main(void)
{
int number, count;
puts("请输入一个整数: ");
while(scanf("%d", &number) == 1)
{
puts("请输入一个位的位置: ");
while(scanf("%d", &count) != 1 || count < 0 || count > 31)
{
printf("您输入的不是一个数字，或者范围不在%d到%d之间\n", 0, CHAR_BIT * sizeof(int) - 1);
printf("请您重新输入: \n");
while(getchar() != '\n')
continue;
}
if(fun_itobs(number, count))
printf("%d在位%d上的值是1\n", number, count);
else
printf("%d在位%d上的值是0\n", number, count);
puts("请输入一个整数: ");
}
puts("Bye!");
return 0;
}
int fun_itobs(int n, int index)
{
int i, ret_val;
static int size = CHAR_BIT * sizeof(int);
char ps[size + 1];
for(i = size - 1; i >= 0; i--, n >>= 1)
ps[i] = (01 & n) + '0';
ps[size] = '\0';
if(ps[size - 1 - index] == '1')
ret_val = 1;
else
ret_val = 0;
return ret_val;
}
5、（借鉴http://ptgmedia.pearsoncmg.com/images/9780321928429/downloads/9780321928429_ProgrammingExerciseAnswers_Selected.pdf的做法，因为实在没想到）
#include <stdio.h>
#include <limits.h> // for CHAR_BIT 一个char的位数
char * itobs(int n, char * ps);
unsigned int rotate_1(unsigned int, unsigned int);
int main(void)
{
char bin_str1[CHAR_BIT * sizeof(int) + 1];
char bin_str2[CHAR_BIT * sizeof(int) + 1];
unsigned int number, count, result;
printf("Enter an integer (q to quit): \n");
while(scanf("%d", &number))
{
printf("Enter the number of bits to be rotated: \n");
if(scanf("%d", &count) != 1)
break;
result = rotate_1(number, count);
itobs(number, bin_str1);
itobs(result, bin_str2);
printf("%u rotated is %u.\n", number, result);
printf("%s rotated is %s.\n", bin_str1, bin_str2);
printf("Enter an integer (q to quit): \n");
}
puts("Bye!");
return 0;
}
char * itobs(int n, char * ps)
{
int i;
const static int size = CHAR_BIT * sizeof(int);
for(i = size - 1; i >= 0; i--, n >>= 1)
ps[i] = (01 & n) + '0';
ps[size] = '\0';
return ps;
}
unsigned int rotate_1(unsigned int n, unsigned int b)
{
static const int size = CHAR_BIT * sizeof(int);
unsigned int overflow;
b %= size;
overflow = n >> (size - b);
return (n << b) | overflow; // 没想到这点
}
6、（全部是自己写的，完美实现！！！）
#include <stdio.h>
#include <string.h>
/* 字体是否粗体 */
#define BOLD_ON 1
#define BOLD_OFF 0
/* 字体对齐方式 */
#define LEFT 0
#define RIGHT 1
#define CENTER 2
/* 字体是否斜体 */
#define ITALIC_ON 1
#define ITALIC_OFF 0
/* 字体是否有下划线 */
#define UNDERLINE_ON 1
#define UNDERLINE_OFF 0
#define MASK 0xFFFFFF00
#define MASK1 0xFFFF80FF
struct font {
unsigned int font_id : 8;
unsigned int font_size : 7;
unsigned int : 1;
unsigned int alignment : 2;
unsigned int bold : 1;
unsigned int italic : 1;
unsigned int underline : 1;
unsigned int : 3;
};
void show(const struct font * ft);
int getlet(const char *);
int getmenu(void);
void eatline(void);
int main(void)
{
/* 初始化font结构 */
struct font ft = {1, 12, LEFT, BOLD_OFF, ITALIC_OFF, UNDERLINE_OFF};
int choice;
int id, size, align;
show(&ft);
putchar('\n');
while((choice = getmenu()) != 'q')
{
switch(choice)
{
case 'f': printf("Enter font id (0-255): ");
while(scanf("%d", &id) != 1 || id < 0 || id > 255)
{
printf("您输入的不是一个整数，或者范围不在0到255之间\n");
while(getchar() != '\n');
continue;
printf("Enter font id (0-255): ");
}
eatline();
ft.font_id = (ft.font_id & MASK) | id;
putchar('\n');
show(&ft);
break;
case 's': printf("Enter font size (0-127): ");
while(scanf("%d", &size) != 1 || size < 0 || size > 255)
{
printf("您输入的不是一个整数，或者范围不在0到127之间\n");
while(getchar() != '\n');
continue;
printf("Enter font size (0-127): ");
}
eatline();
ft.font_size = ((ft.font_size & MASK1) >> 8) | size;
putchar('\n');
show(&ft);
break;
case 'a': printf("Select alignment: \n");
puts("l) left c) center r)right");
align = getlet("lcr");
switch(align)
{
case 'l': ft.alignment = LEFT;
break;
case 'c': ft.alignment = CENTER;
break;
case 'r': ft.alignment = RIGHT;
break;
}
putchar('\n');
show(&ft);
break;
case 'b': ft.bold = BOLD_ON;
putchar('\n');
show(&ft);
break;
case 'i': ft.italic = ITALIC_ON;
putchar('\n');
show(&ft);
break;
case 'u': ft.underline = UNDERLINE_ON;
putchar('\n');
show(&ft);
break;
}
}
puts("Bye!");
return 0;
}
void show(const struct font * ft)
{
printf("ID\tSIZE\tALIGNMENT\tB\tI\tU\n");
printf("%d\t%d", ft->font_id, ft->font_size);
switch(ft->alignment)
{
case LEFT: printf("%10s", "left");
break;
case RIGHT: printf("%10s", "right");
break;
case CENTER: printf("%10s", "center");
break;
default: printf("unknown alignment");
}
printf("%14s%8s%8s\n", ft->bold == BOLD_OFF? "off" : "on",
ft->italic == ITALIC_OFF? "off" : "on",
ft->underline == UNDERLINE_OFF? "off" : "on");
}
int getlet(const char * s)
{
char c;
c = getchar();
while(strchr(s, c) == NULL)
{
printf("请您在%s这串字符串中输入一个字符: \n", s);
while(getchar() != '\n')
continue;
c = getchar();
}
while(getchar() != '\n')
continue;
return c;
}
int getmenu(void)
{
int i;
const char * str[7] = {
"change font",
"change size",
"change alignment",
"toggle bold",
"toggle italic",
"toggle underline",
"quit"
};
const char pstr[8] = "fsabiuq";
for(i = 0; i < 7; i++)
{
printf("%c) %s ", pstr[i], str[i]);
if(i % 3 == 2)
putchar('\n');
}
if(i % 3 != 0)
putchar('\n');
return getlet(pstr);
}
void eatline(void)
{
while(getchar() != '\n')
continue;
}
7、（有大问题，明天再看！！！借鉴
http://ptgmedia.pearsoncmg.com/images/9780321928429/downloads/9780321928429_ProgrammingExerciseAnswers_Selected.pdf但是程序也有问题）
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define LEFT 0x00000
#define CENTER 0x08000
#define RIGHT 0x10000
#define BOLD 0x20000
#define UNDERLINE 0x80000
#define ID_MASK 0xFF
#define SIZE_MASK 0x7F00
#define ALIGN_MASK 0x18000
#define ITALIC 0x40000
#define SIZE_SHIFT 8
typedef unsigned long font;
char do_menu(font * f); // f为一个指向unsigned long的指针
void show_font(font f);
char get_choice(const char *);
void show_menu(void);
void eatline(void);
void get_id(font * f);
void get_size(font * f);
void get_align(font * f);
int main(void)
{
font sample = 1 | (12 << SIZE_SHIFT) | LEFT | ITALIC; // sample = 0100 0000 1100 0000 0001(斜体,没有预留空隙)
while(do_menu(&sample) != 'q')
continue;
puts("Bye!");
return 0;
}
char do_menu(font * f)
{
char response;
show_font(*f);
show_menu();
response = get_choice("fsabiuq");
switch(response)
{
case 'f': get_id(f); break;
case 's': get_size(f); break;
case 'a': get_align(f); break;
case 'b': *f ^= BOLD; break;
case 'i': *f ^= ITALIC; break;
case 'u': *f ^= UNDERLINE; break;
case 'q': break;
default: printf("menu problem\n");
}
return response;
}
void show_font(font f)
{
printf("\n%4s %4s %9s %3s %3s %3s\n", "ID", "SIZE", "ALIGNMENT", "B", "I", "U");
printf("%4lu %4lu", f & ID_MASK, (f & SIZE_MASK) >> SIZE_SHIFT);
switch(f & ALIGN_MASK)
{
case LEFT: printf("%7s", "left"); break;
case CENTER: printf("%7s", "center"); break;
case RIGHT: printf("%7s", "right"); break;
default: printf("%7s", "known"); break;
}
printf("%8s %3s %3s\n\n", (f & BOLD) == BOLD ? "on" : "off",
(f & ITALIC) == ITALIC ? "on" : "off",
(f & UNDERLINE) == UNDERLINE ? "on" : "off");
}
char get_choice(const char * s)
{
char ch;
ch = getchar();
ch = tolower(ch);
while(strchr(s, ch) == NULL)
{
printf("Please enter one of the following: %s\n", s);
eatline();
ch = tolower(getchar());
}
eatline();
return ch;
}
void eatline(void)
{
while(getchar() != '\n')
continue;
}
void show_menu(void)
{
puts("f) change font s) change size a) change alignment");
puts("b) toggle bold i) toggle italic u) toggle underline");
puts("q) quit");
}
void get_id(font * f)
{
int id;
printf("Enter font id (0-255): ");
scanf("%d", &id);
id = id & ID_MASK;
//*f |= id;
*f = (*f & 0xFFF00) | id; // 相应位要先置为0之后再用|运算符吧！！！（问题出现在这）
eatline();
}
void get_size(font * f)
{
int size;
printf("Enter font size (0-127): ");
scanf("%d", &size);
*f &= (0xF8011);
*f |= (size << SIZE_SHIFT) & SIZE_MASK;
eatline();
}
void get_align(font * f)
{
printf("Select alignment: \n");
printf("l) left c) center r) right\n");
switch(get_choice("lcr"))
{
case 'l': *f &= ~ALIGN_MASK;
*f |= LEFT;
break;
case 'c': *f &= ~ALIGN_MASK;
*f |= CENTER;
break;
case 'r': *f &= ~ALIGN_MASK;
*f |= RIGHT;
break;
default: printf("alignment problem\n");
}
}