学完C语言之后，我就去阅读《C Primer Plus》这本经典的C语言书籍，对每一章的编程练习题都做了相关的解答，仅仅代表着我个人的解答思路，如有错误，请各位大佬帮忙点出！
由于使用的是命令行参数常用于linux系统或者vscode，但此代码是运行于vs2022的，测试截图就不弄了。
1.编写一个函数，把二进制字符串转换为一个数值。例如，有下面的语 句：
char * pbin = "01001001";
那么把pbin作为参数传递给该函数后，它应该返回一个int类型的值25。
#include <stdio.h>
#include <string.h>
int convert(const char* str)
{int sum = 0, len = strlen(str);for (int i = len - 1, exp = 1; i >= 0; --i, exp *= 2){sum += (str[i] - '0') * exp;}return sum;
}
int main(void)
{const char* pbin = "01001001";printf("binary %s is decimal %d\n", pbin, convert(pbin));return 0;
}
2.编写一个程序，通过命令行参数读取两个二进制字符串，对这两个二 进制数使用～运算符、&运算符、|运算符和^运算符，并以二进制字符串形 式打印结果（如果无法使用命令行环境，可以通过交互式让程序读取字符 串）。
#include <stdio.h>
#include <stdlib.h>
int bstr_to_dec(const char* str)
{int val = 0;while (*str){val = val * 2 + (*str++) - '0';}return val;
}
char* itobs(int n, char* str)
{int sz = 8 * sizeof(int);for (int i = sz - 1; i >= 0; --i, n >>= 1){str[i] = (n & 1) + '0';}str[sz] = '\0';return str;
}
int main(int argc, char* argv[])
{char bstr[8 * sizeof(int) + 1];char str1[20] = {0};char str2[20] = { 0 };printf("请输入两个字符串:");scanf("%s%s", str1, str2);int v1 = bstr_to_dec(str1);int v2 = bstr_to_dec(str2);printf("~%s = %s\n", str1, itobs(~v1, bstr));printf("~%s = %s\n", str2, itobs(~v2, bstr));printf("%s & %s = %s\n", str1, str2, itobs(v1 & v2, bstr));printf("%s | %s = %s\n", str1, str2, itobs(v1 | v2, bstr));printf("%s ^ %s = %s\n", str1, str2, itobs(v1 ^ v2, bstr));return 0;
}
3.编写一个函数，接受一个 int 类型的参数，并返回该参数中打开位的 数量。在一个程序中测试该函数。
#include <stdio.h>
char* itobs(int n, char* str)
{int sz = 8 * sizeof(int);for (int i = sz - 1; i >= 0; --i, n >>= 1){str[i] = (n & 1) + '0';}str[sz] = '\0';return str;
}
int onbits(int x)
{int sum = 0;for (int i = 8 * sizeof(int) - 1; i >= 0; --i){sum += (x >> i) & 1;}return sum;
}
int main(int argc, char* argv[])
{int x = 11;char bstr[8 * sizeof(int) + 1];printf("%d(%s) has %d bit on.\n", x, itobs(x, bstr), onbits(x));return 0;
}
4.编写一个程序，接受两个int类型的参数：一个是值；一个是位的位 置。如果指定位的位置为1，该函数返回1；否则返回0。在一个程序中测试 该函数。
#include <stdio.h>
int test_bit(int x, int pos)
{return (x >> pos) & 1;
}
char* itobs(int n, char* str)
{int sz = 8 * sizeof(int);for (int i = sz - 1; i >= 0; --i, n >>= 1){str[i] = (n & 1) + '0';}str[sz] = '\0';return str;
}
int main(int argc, char* argv[])
{int x = 11;int sz = 8 * sizeof(int);char bstr[8 * sizeof(int) + 1];printf("%d(%s):\n", x, itobs(x, bstr));for (int i = sz - 1; i >= 0; --i){printf("The position %d is %d\n", i + 1, test_bit(x, i));}return 0;
}
5.编写一个函数，把一个 unsigned int 类型值中的所有位向左旋转指定数 量的位。例如，rotate_l(x, 4)把x中所有位向左移动4个位置，而且从最左端 移出的位会重新出现在右端。也就是说，把高阶位移出的位放入低阶位。在 一个程序中测试该函数。
#include <stdio.h>
char* itobs(int n, char* str)
{int sz = 8 * sizeof(int);for (int i = sz - 1; i >= 0; --i, n >>= 1){str[i] = (n & 1) + '0';}str[sz] = '\0';return str;
}
unsigned int rotate_l(unsigned int n, unsigned int b)
{static const int size = 8 * sizeof(int);b %= size;return (n << b) | (n >> (size - b));
}
int main(int argc, char* argv[])
{unsigned int val = 11;unsigned int rot = rotate_l(val, 4);char bstr1[8 * sizeof(int) + 1];char bstr2[8 * sizeof(int) + 1];printf("%u rotated is %u.\n", val, rot);printf("%s rotated is %s.\n", itobs(val, bstr1), itobs(rot, bstr2));return 0;
}
6.设计一个位字段结构以储存下面的信息。
字体ID：0～255之间的一个数；
字体大小：0～127之间的一个数；
对齐：0～2之间的一个数，表示左对齐、居中、右对齐；
加粗：开（1）或闭（0）；
斜体：开（1）或闭（0）；
在一个程序中使用该结构来打印字体参数，并使用循环菜单来让用户改 变参数。例如，该程序的一个运行示例如下：
该程序要使用按位与运算符（&）和合适的掩码来把字体ID和字体大小 信息转换到指定的范围内。
#include <stdio.h>
#include <ctype.h>
#include <string.h>typedef unsigned int uint;
typedef struct
{uint id : 8;uint sz : 7;uint at : 2;uint b : 1;uint i : 1;uint u : 1;
} font;static font ft = { 1, 12, 0, 0, 0, 0 };
const char* state[4] = { "off", "on" };
const char* alignment[7] = { "left", "center", "right" };
void eatline(void)
{while (getchar() != '\n')continue;
}
int get_first(void)
{int ch;do{ch = getchar();} while (isspace(ch));eatline();return ch;
}
int get_choice(void)
{int ch;printf("ID SIZE ALIGNMENT B I U\n");printf("%-7u%-9u%-12s", ft.id, ft.sz, alignment[ft.at]);printf("%-8s%-8s%-8s\n", state[ft.b], state[ft.i], state[ft.u]);printf("f) change font s) change size a) change alignment\n");printf("b) toggle bold i) toggle italic u) toggle underline\n");printf("q) quit\n");while (ch = get_first(), NULL == strchr("fsabiuq", ch)){printf("Please enter with f, s, a, b, i, u or q: ");}return ch;
}
void change_font(void)
{int ch;uint id;printf("Enter font id (0-255): ");while (scanf("%u", &id) != 1){while ((ch = getchar()) != '\n'){putchar(ch);}printf(" is not a id.\n");printf("Please enter a number such as 0, 5 or 255: ");}ft.id = id & 0XFF;
}
void change_size(void)
{int ch;uint sz;printf("Enter font sz (0-127): ");while (scanf("%u", &sz) != 1){while ((ch = getchar()) != '\n'){putchar(ch);}printf(" is not a size.\n");printf("Please enter a number such as 0, 5 or 127: ");}ft.sz = sz & 0x7F;
}
void change_alignment(void)
{int ch;printf("Select alignment:\n");printf("l) left c) center r) right\n");while (ch = get_first(), NULL == strchr("lcr", ch)){printf("Please enter with l, c or r: ");}ft.at = (ch == 'l' ? 0 : ch == 'c' ? 1 : 2);
}
void change_toggle(int ch)
{if (ch == 'b'){ft.b ^= 1;}else if (ch == 'i'){ft.i ^= 1;}else{ft.u ^= 1;}
}
int main(void)
{int ch;while ((ch = get_choice()) != 'q'){switch (ch){case 'f':{change_font();break;}case 's':{change_size();break;}case 'a':{change_alignment();break;}case 'b':case 'i':case 'u':{change_toggle(ch);break;}}putchar('\n');}printf("Bye!\n");return 0;
}
7.编写一个与编程练习 6 功能相同的程序，使用 unsigned long 类型的变 量储存字体信息，并且使用按位运算符而不是位成员来管理这些信息。
#include <stdio.h>
#include <ctype.h>
#include <string.h>
typedef unsigned long ulong;
static ulong ft = 0x00001180;
const char* state[4] = { "off", "on" };
const char* alignment[7] = { "left", "center", "right" };
void eatline(void)
{while (getchar() != '\n')continue;
}
int get_first(void)
{int ch;do{ch = getchar();} while (isspace(ch));eatline();return ch;
}
int get_choice(void)
{int ch;printf("ID SIZE ALIGNMENT B I U\n");printf("%-7u%-9u%-12s", (ft >> 12) & 0XFF, (ft >> 5) & 0x7F, alignment[(ft >> 3) & 0x03]);printf("%-8s%-8s%-8s\n", state[(ft >> 2) & 1], state[(ft >> 1) & 1], state[ft & 1]);printf("f) change font s) change size a) change alignment\n");printf("b) toggle bold i) toggle italic u) toggle underline\n");printf("q) quit\n");while (ch = get_first(), NULL == strchr("fsabiuq", ch)){printf("Please enter with f, s, a, b, i, u or q: ");}return ch;
}
void change_font(void)
{int ch;ulong id;printf("Enter font id (0-255): ");while (scanf("%lu", &id) != 1){while ((ch = getchar()) != '\n'){putchar(ch);}printf(" is not a id.\n");printf("Please enter a number such as 0, 5 or 255: ");}id &= 0XFF, id <<= 12;for (int i = 12; i < 20; ++i){ft &= ~(ulong)(1 << i);}ft |= id;
}
void change_size(void)
{int ch;ulong sz;printf("Enter font sz (0-127): ");while (scanf("%lu", &sz) != 1){while ((ch = getchar()) != '\n'){putchar(ch);}printf(" is not a size.\n");printf("Please enter a number such as 0, 5 or 127: ");}sz &= 0X7F, sz <<= 5;for (int i = 5; i < 12; ++i){ft &= ~(ulong)(1 << i);}ft |= sz;
}
void change_alignment(void)
{int ch;printf("Select alignment:\n");printf("l) left c) center r) right\n");while (ch = get_first(), NULL == strchr("lcr", ch)){printf("Please enter with l, c or r: ");}ft &= ~(ulong)(1 << 3), ft &= ~(ulong)(1 << 4);ft = ft | (ch == 'c' ? (ulong)(1 << 3) : ch == 'r' ? (ulong)(1 << 4) : 0);
}
void change_toggle(int ch)
{if (ch == 'b'){if (ft & 0x04){ft &= ~(ulong)(0x04);}else{ft |= (ulong)(0x04);}}else if (ch == 'i'){if (ft & 0x02){ft &= ~(ulong)(0x02);}else{ft |= (ulong)(0x02);}}else{if (ft & 0x01){ft &= ~(ulong)(0x01);}else{ft |= (ulong)(0x01);}}
}
int main(void)
{int ch;while ((ch = get_choice()) != 'q'){switch (ch){case 'f':{change_font();break;}case 's':{change_size();break;}case 'a':{change_alignment();break;}case 'b':case 'i':case 'u':{change_toggle(ch);break;}}putchar('\n');}printf("Bye!\n");return 0;
}
