C Primer Plus第十三章编程练习答案

news/2024/10/30 18:13:58/

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.修改程序清单13.1中的程序,要求提示用户输入文件名,并读取用户 输入的信息,不使用命令行参数。

#include <stdio.h>
#include <stdlib.h>
#define LEN 50
int main(int argc, char* argv[])
{int ch;FILE* fp;int count = 0;char filename[LEN];printf("Please enter a filename: ");scanf("%s", filename);fp = fopen(filename, "r");if (fp == NULL){printf("Can't open %s\n", filename);exit(0);}while ((ch = getc(fp)) != EOF){putc(ch, stdout);count++;}fclose(fp);printf("\nFile %s has %d characters\n", filename, count);return 0;
}

2.编写一个文件拷贝程序,该程序通过命令行获取原始文件名和拷贝文 件名。尽量使用标准I/O和二进制模式。

#include <stdio.h>
#include <stdlib.h>
#define BUF 512
int main(int argc, char* argv[])
{int bytes;FILE* source;FILE* target;char temp[BUF];if ((source = fopen("test.txt", "rb")) == NULL){printf("Can't open %s\n", "test.txt");exit(0);}if ((target = fopen("copy.txt", "wb")) == NULL){printf("Can't open %s\n", "copy.txt");exit(0);}while ((bytes = fread(temp, sizeof(char), BUF, source)) > 0){fwrite(temp, sizeof(char), bytes, target);}fclose(source);fclose(target);return 0;
}

3.编写一个文件拷贝程序,提示用户输入文本文件名,并以该文件名作 为原始文件名和输出文件名。该程序要使用 ctype.h 中的 toupper()函数,在 写入到输出文件时把所有文本转换成大写。使用标准I/O和文本模式。

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#define LEN 50
int main(int argc, char* argv[])
{int ch;FILE* fp;char filename[LEN];printf("Please enter a filename: ");scanf("%s", filename);fp = fopen(filename, "r+");if (fp == NULL){printf("Can't open %s\n", filename);exit(0);}while ((ch = getc(fp)) != EOF){fseek(fp, -1L, SEEK_CUR);putc(toupper(ch), fp);fseek(fp, 0L, SEEK_CUR); rewind(fp);printf("File %s:\n", filename);while ((ch = getc(fp)) != EOF){putchar(ch);}printf("\n");fclose(fp);return 0;
}

4.编写一个程序,按顺序在屏幕上显示命令行中列出的所有文件。使用 argc控制循环。

#include <stdio.h>
#include <stdlib.h>
int main(int argc, char* argv[])
{int i, temp;FILE* source;if (argc == 1){printf("Usage: %s filename[s]\n", argv[0]);exit(0);}for (i = 1; i < argc; i++){source = fopen(argv[i], "r");if (source == NULL){printf("Can't open file %s\n", argv[i]);continue;}printf("File %s:\n", argv[i]);while ((temp = getc(source)) != EOF){putchar(temp);}printf("\n");fclose(source);}return 0;
}

5.修改程序清单13.5中的程序,用命令行界面代替交互式界面。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFSIZE 4096
#define SLEN 81
void append(FILE* source, FILE* dest)
{size_t bytes;static char temp[BUFSIZE];while ((bytes = fread(temp, sizeof(char), BUFSIZE, source)) > 0){fwrite(temp, sizeof(char), bytes, dest);}return;
}
int main(int argc, char* argv[])
{int i, ch;int files = 0;FILE* fa;FILE* fs;if (argc < 3){printf("Usage: %s appendfile sourcefile.\n", argv[0]);exit(0);}if ((fa = fopen(argv[1], "a+")) == NULL){printf("Can't open %s\n", argv[1]);exit(0);}if (setvbuf(fa, NULL, _IOFBF, BUFSIZE) != 0){fputs("Can't create output buffer\n", stderr);exit(0);}for (i = 2; i < argc; i++){if (strcmp(argv[i], argv[1]) == 0){fputs("Can't append file to itself\n", stderr);}else if ((fs = fopen(argv[i], "r")) == NULL){printf("Can't open %s\n", argv[i]);}else{if (setvbuf(fs, NULL, _IOFBF, BUFSIZE) != 0){fputs("Can't create input buffer\n", stderr);continue;}append(fs, fa);if (ferror(fs) != 0){printf("Error in reading file %s.\n", argv[i]);}if (ferror(fa) != 0){printf("Error in writing file %s.\n", argv[1]);}fclose(fs);files++;printf("File %s appended.\n", argv[i]);}}printf("Done appending. %d files appended.\n", files);rewind(fa); printf("%s contents:\n", argv[1]);while ((ch = getc(fa)) != EOF){putchar(ch);}printf("\n");printf("Done displaying.");fclose(fa);return 0;
}

6.使用命令行参数的程序依赖于用户的内存如何正确地使用它们。重写 程序清单 13.2 中的程序,不使用命令行参数,而是提示用户输入所需信 息。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LEN 40
int main(int argc, char* argv[])
{FILE* in, * out;int ch;char name[LEN];int count = 0;char temp[LEN];printf("Please enter a filename:\n");scanf("%s", temp);in = fopen(temp, "r");if (in == NULL){printf("I could't open the file \"%s\"\n", temp);exit(0);}strncpy(name, temp, LEN - 5);name[LEN - 5] = '\0';strcat(name, ".red");out = fopen(name, "w");if (out == NULL){printf("Can't create output file.\n");exit(1);}while ((ch = getc(in)) != EOF){if (count++ % 3 == 0){putc(ch, out);}}fclose(in);fclose(out);return 0;
}

7.编写一个程序打开两个文件。可以使用命令行参数或提示用户输入文 件名。

a.该程序以这样的顺序打印:打印第1个文件的第1行,第2个文件的第1 行,第1个文件的第2行,第2个文件的第2行,以此类推,打印到行数较多文 件的最后一行。

b.修改该程序,把行号相同的行打印成一行。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define LEN 256
int main(int argc, char* argv[])
{FILE* f1;FILE* f2;char str1[LEN], str2[LEN];printf("请输入两个文件的名字:");scanf("%s %s", str1, str2);f1 = fopen(str1, "r");if (f1 == NULL){printf("Can't open file %s\n", str1);exit(0);}f2 = fopen(str2, "r");if (f2 == NULL){printf("Can't open file %s\n", str2);exit(0);}char* s1 = fgets(str1, LEN, f1);char* s2 = fgets(str2, LEN, f2);while (s1 || s2){int len1 = strlen(str1), len2 = strlen(str2);if (str1[len1 - 1] == '\n'){str1[len1 - 1] = '\0';}if (str2[len2 - 1] == '\n'){str2[len2 - 1] = '\0';}if (s1){printf("%s\n", str1);}if (s2){printf("%s\n", str2);}s1 = fgets(str1, LEN, f1), s2 = fgets(str2, LEN, f2);}fclose(f1);fclose(f2);return 0;
}

8.编写一个程序,以一个字符和任意文件名作为命令行参数。如果字符 后面没有参数,该程序读取标准输入;否则,程序依次打开每个文件并报告 每个文件中该字符出现的次数。文件名和字符本身也要一同报告。程序应包 含错误检查,以确定参数数量是否正确和是否能打开文件。如果无法打开文件,程序应报告这一情况,然后继续处理下一个文件。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int search(int ch, FILE* fp)
{int find;int n = 0;while ((find = getc(fp)) != EOF){if (ch == find){++n;}}return n;
}
int main(int argc, char* argv[])
{FILE* fp;int i, ch, ct;int count = 0;if (argc < 2){printf("Usage: %s character filename[s]\n", argv[0]);exit(-1);}if (strlen(argv[1]) != 1){printf("The second argument must be a character!\n");exit(-1);}if (argc == 2){fp = stdin;ch = argv[1][0];printf("Please enter a string (EOF to quit): ");count = search(ch, fp);printf("%c appeared %d times.\n", ch, count);}else if (argc > 2){ch = argv[1][0];for (i = 2; i < argc; i++){if ((fp = fopen(argv[i], "r")) == NULL){printf("Can't open file %s\n", argv[i]);continue;}printf("File %s:\n", argv[i]);while ((ct = getc(fp)) != EOF){putchar(ct);}rewind(fp);count = search(ch, fp);printf("%c appeared %d times in file %s\n", ch, count, argv[i]);fclose(fp);}}return 0;
}

9.修改程序清单 13.3 中的程序,从 1 开始,根据加入列表的顺序为每个 单词编号。当程序下次运行时,确保新的单词编号接着上次的编号开始。

#include <stdio.h>
#include <stdlib.h>
#define MAX 41
int main(void)
{FILE* fp;int ct = 0;char words[MAX];fp = fopen("wordy.txt", "a+");if ( fp == NULL){printf("Can't open \"wordy\" file.\n");exit(-1);}while (fgets(words, MAX, fp) != NULL){ct++;}rewind(fp);printf("Enter words to add to the file; press the #\n");printf("key at the beginning of a line to terminate.\n");while ((fscanf(stdin, "%s", words) == 1) && (words[0] != '#')){fprintf(fp, "%-2d : %s\n", ++ct, words);}printf("File contents:");rewind(fp);while (fgets(words, MAX, fp) != NULL){fputs(words, stdout);}printf("Done!\n");fclose(fp);return 0;
}

10.编写一个程序打开一个文本文件,通过交互方式获得文件名。通过 一个循环,提示用户输入一个文件位置。然后该程序打印从该位置开始到下 一个换行符之前的内容。用户输入负数或非数值字符可以结束输入循环。

#include <stdio.h>
#include <stdlib.h>
#define LEN 50int main(int argc, char* argv[])
{int ch;FILE* fp;int number;char filename[LEN];printf("Please enter a filename: ");scanf("%49s", filename);fp = fopen(filename, "r");if ( fp == NULL){printf("Can't open file %s\n", filename);exit(-1);}printf("Please enter a file position (<0 or q to quit): ");while (scanf("%d", &number) == 1 && number >= 0){fseek(fp, number, SEEK_SET);while ((ch = getc(fp)) != '\n' && ch != EOF){putchar(ch);}if (ch == EOF){printf("The position reaches EOF.\n");break;}printf("\nYou can enter again (<0 or q to quit): ");}printf("Done.\n");fclose(fp);return 0;
}

11.编写一个程序,接受两个命令行参数。第1个参数是一个字符串,第 2个参数是一个文件名。然后该程序查找该文件,打印文件中包含该字符串 的所有行。因为该任务是面向行而不是面向字符的,所以要使用fgets()而不 是getc()。使用标准C库函数strstr()(11.5.7节简要介绍过)在每一行中查找 指定字符串。假设文件中的所有行都不超过255个字符。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SLEN 256
int main(int argc, char* argv[])
{FILE* fp;char line[SLEN];if (argc != 3){printf("Usage: %s string filename\n", argv[0]);exit(-1);}if ((fp = fopen(argv[2], "r")) == NULL){printf("Can't open file %s", argv[2]);exit(-1);}while (fgets(line, SLEN, fp) != NULL){if (strstr(line, argv[1]) != NULL){fputs(line, stdout);}}fclose(fp);return 0;
}

12.创建一个文本文件,内含20行,每行30个整数。这些整数都在0~9 之间,用空格分开。该文件是用数字表示一张图片,0~9表示逐渐增加的灰 度。编写一个程序,把文件中的内容读入一个20×30的int数组中。一种把这 些数字转换为图片的粗略方法是:该程序使用数组中的值初始化一个20×31 的字符数组,用值0 对应空格字符,1 对应点字符,以此类推。数字越大表 示字符所占的空间越大。例如,用#表示9。每行的最后一个字符(第31个) 是空字符,这样该数组包含了20个字符串。最后,程序显示最终的图片 (即,打印所有的字符串),并将结果储存在文本文件中。例如,下面是开 始的数据:

 

 

#include <stdio.h>
#include <stdlib.h>
#define ROWS 20
#define COLS 30
#define LEVELS 10
#define LEN 50
const char trans[LEVELS + 1] = " .':~*=&%#"; 
void change(int(*a)[COLS], char(*b)[COLS], int rows)
{int row, col;for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){b[row][col] = trans[a[row][col]];}}
}
int main(void)
{int row, col;FILE* infile;char filename[LEN];int figure[ROWS][COLS];char picture[ROWS][COLS];printf("Please enter a filename: ");scanf("%s", filename);infile = fopen(filename, "r+");if ( infile == NULL){printf("Can't open file %s\n", filename);exit(-1);}for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){fscanf(infile, "%d", &figure[row][col]);}}change(figure, picture, ROWS);printf("File %s have been transformed pictures:\n", filename);for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){putchar(picture[row][col]);}printf("\n");}fseek(infile, 0L, SEEK_END);putc('\n', infile);      for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){fprintf(infile, "%c", picture[row][col]);}putc('\n', infile);}fclose(infile);return 0;
}

13.用变长数组(VLA)代替标准数组,完成编程练习12。

#include <stdio.h>
#include <stdlib.h>
#define ROWS 20
#define COLS 30
#define LEVELS 10
#define LEN 50
const char trans[LEVELS + 1] = " .':~*=&%#";
void change(int rows, int cols, int a[rows][cols], char b[rows][cols])
{int row, col;for (row = 0; row < rows; row++){for (col = 0; col < cols; col++){b[row][col] = trans[a[row][col]];}}return;
}
int main(void)
{int row, col;FILE* infile;char filename[LEN];int figure[ROWS][COLS];char picture[ROWS][COLS];printf("Please enter a filename: ");scanf("%s", filename);infile = fopen(filename, "r+");if ( infile == NULL){printf("Can't open file %s\n", filename);exit(-1);}for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){fscanf(infile, "%d", &figure[row][col]);}}change(ROWS, COLS, figure, picture);printf("File %s have been transformed pictures:\n", filename);for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){putchar(picture[row][col]);}printf("\n");}fseek(infile, 0L, SEEK_END);putc('\n', infile);     for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){fprintf(infile, "%c", picture[row][col]);}putc('\n', infile);}fclose(infile);return 0;
}

14.数字图像,尤其是从宇宙飞船发回的数字图像,可能会包含一些失 真。为编程练习12添加消除失真的函数。该函数把每个值与它上下左右相邻 的值作比较,如果该值与其周围相邻值的差都大于1,则用所有相邻值的平 均值(四舍五入为整数)代替该值。注意,与边界上的点相邻的点少于4 个,所以做特殊处理。

#include <stdio.h>
#include <stdlib.h>
#define ROWS 20
#define COLS 30
#define LEVELS 10
#define LEN 50
const char trans[LEVELS + 1] = " .':~*=&%#";
int clean_distortion(int(*a)[COLS], int rows, int x, int y)
{int i = 0, average = 0, cnt = 0, sur = 0;int d[4][2] = { {0, 1}, {1, 0}, {0, -1}, {-1, 0} };for (i = 0; i < 4; ++i){int dx = x + d[i][0], dy = y + d[i][1];if (dx < 0 || dx >= ROWS || dy < 0 || dy >= COLS) continue;++sur;if (a[x][y] - a[dx][dy] > 1){++cnt, average += a[dx][dy];}}if (cnt != sur) return a[x][y];return 1.0 * average / cnt + 0.5;
}
void change(int(*a)[COLS], char(*b)[COLS], int rows)
{int row, col;for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){b[row][col] = trans[a[row][col]];}}
}
int main(void)
{int row, col;FILE* infile;char filename[LEN];int figure[ROWS][COLS];char picture[ROWS][COLS];printf("Please enter a filename: ");scanf("%s", filename);infile = fopen(filename, "r+");if ( infile == NULL){printf("Can't open file %s\n", filename);exit(-1);}for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){fscanf(infile, "%d", &figure[row][col]);}}for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){figure[row][col] = clean_distortion(figure, ROWS, row, col);}}change(figure, picture, ROWS);printf("File %s have been transformed pictures:\n", filename);for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){putchar(picture[row][col]);}printf("\n");}fseek(infile, 0L, SEEK_END);putc('\n', infile);for (row = 0; row < ROWS; row++){for (col = 0; col < COLS; col++){fprintf(infile, "%c", picture[row][col]);}putc('\n', infile);}fclose(infile);return 0;
}

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