《C和指针》章节后编程练习解答参考——第9章

9.1

 #include <stdio.h>
 #include <ctype.h>
 #include <string.h>

 #define  N  100

 int main (void)
 {
     int i = ;
     char strarray[N+]; //= "Hello world!    \t3I'm here!";
     char *input = strarray;
     char ch;
     unsigned int cont = ;
     int ctr=, spc=, num=, low=, upp=, puc=, upr=;
     float ctrf=, spcf=, numf=, lowf=, uppf=, pucf=, uprf=;

     printf("Please enter a string:\n");

     while (( ch = getchar() ) != '\n')
     {
         *(input + i) = ch;
         i++;
     }
     *(input + i) = '\0';
     cont = strlen(input);

     while (*input != '\0')
     {
         if (iscntrl(*input))
             ctr++;
         if (isspace(*input))
             spc++;
         if (isdigit(*input))
             num++;
         if (islower(*input))
             low++;
         if (isupper(*input))
             upp++;
         if (ispunct(*input))
             puc++;
         if (!(isprint(*input)))
             upr++;
         input++;
     }

     printf("\nTotle char number is: Count = %d\n", cont);
     printf("cntrl = %d,\tspace = %d,\tdigit = %d\n", ctr, spc, num);
     printf("lower = %d,\tupper = %d,\tpunct = %d\n", low, upp, puc);
     printf("uprint = %d\n", upr);

     ctrf = (float)ctr/(float)cont;
     spcf = (float)spc/(float)cont;
     numf = (float)num/(float)cont;
     lowf = (float)low/(float)cont;
     uppf = (float)upp/(float)cont;
     pucf = (float)puc/(float)cont;
     uprf = (float)upr/(float)cont;

     printf("\nHere is the percent of every count:\n");
     printf("cntrl = %.3f%%\nspace = %.3f%%\ndigit = %.3f%%\n",ctrf* , spcf*, numf*);
     printf("lower = %.3f%%\nupper = %.3f%%\npunct = %.3f%%\n", lowf*, uppf*, pucf*);
     printf("uprnt = %.3f%%\n", uprf*);

     getchar();
     return ;
 }

9.3

 #include <stdio.h>
 #include <string.h>

 void my_strcpy(char *dst, char *src)
 {
     size_t len = , dstlen = , srclen = ;
     dstlen = strlen(dst);
     srclen = strlen(src);

     len = ( dstlen >= srclen ? srclen : dstlen );
     strncpy(dst, src, len);
 }

 void show_string(char *str)
 {
     while (*str != '\0')
         printf("%c", *str++);
     putchar('\n');
 }

 int main (void)
 {
     char dst[] = "Hello";
     char src[] = "I'm here!";
     char *dstp = dst;
     char *srcp = src;

     my_strcpy(dstp, srcp);

     show_string(dstp);
     show_string(srcp);

     getchar();
     return ;
 }

9.4

 #include <stdio.h>
 #include <string.h>

 #define  M  12
 #define  N  16

 void my_strcat(char *dst, char *src)
 {
     size_t len = , dstlen = , srclen = , restlen = ;
     dstlen = strlen(dst);
     srclen = strlen(src);

     len = ( (restlen = M - dstlen - ) > srclen ? srclen : restlen );
     strncat(dst, src, len);
 }

 void show_string(char *str)
 {
     while (*str != '\0')
         printf("%c", *str++);
     putchar('\n');
 }

 int main (void)
 {
     char dst[M] = "Hello!";
     char src[N] = "I'm here!";
     char *dstp = dst;
     char *srcp = src;

     my_strcat(dst, src);

     show_string(dstp);
     show_string(srcp);

     getchar();
     return ;
 }

9.5

 #include <stdio.h>
 #include <string.h>

 #define  M  12
 #define  N  16

 void my_strncat(char *dest, char *src, int dest_len)
 {
     size_t len = , dstlen = , srclen = , restlen = ;
     dstlen = strlen(dest);
     srclen = strlen(src);

     len = ( (restlen = dest_len - dstlen - ) > srclen ? srclen : restlen );
     strncat(dest, src, len);
 }

 void show_string(char *str)
 {
     while (*str != '\0')
         printf("%c", *str++);
     putchar('\n');
 }

 int main (void)
 {
     char dst[M] = "Hello!";
     char src[N] = "I'm here!";
     char *dstp = dst;
     char *srcp = src;

     my_strncat(dst, src, M);

     show_string(dstp);
     show_string(srcp);

     getchar();
     return ;
 }

9.6

 #include <stdio.h>
 #include <string.h>

 char *my_strcpy_end(char *dst, char *src)
 {
     int i, dstlen = , srclen = ;

     dstlen = strlen(dst);
     srclen = strlen(src);

     if ( dstlen >= srclen )
         strcpy(dst, src);
     else
         strncpy(dst, src, dstlen);

     for ( i = ; *(dst + i) != '\0'; i++);
     return dst + i;
 }

 int main (void)
 {
     char *p = NULL;
     char dst[] = "Hello world";
     //char src[] = "123456789";
     char src[] = "";

     p = my_strcpy_end(dst, src);

     printf("%c\n", *(p - ));

     getchar();
     return ;
 }

9.8

 #include <stdio.h>
 #include <string.h>

 char *my_strnchr( char const *str, int ch, int which )
 {
     int i;
     char *p = NULL;
     p = str;

     for ( i = ; i < which; i++)
     {
         if ( i != )
             p++;
         p = strchr(p, ch);
     }

     return p;
 }

 int main (void)
 {
     int i;
     char str[] = "Hello world!";
     int chr = 'l';
     int which = ;

     char *find = my_strnchr(str, chr, which);

     for (i = -; i < ; i++)
         printf("%c\t", *(find + i));
     putchar('\n');

     getchar();
     return ;
 }

9.9

 #include <stdio.h>
 #include <string.h>

 int count_chars(char const *str, char const *chars)
 {
     int count = , len = ;
     char *pos = NULL;
     pos = str;

     while (( pos = strpbrk(pos, chars) ) != NULL )
     {
         count++;
         pos++;
     }

     return count;
 }

 int main (void)
 {
     char str[] = "Hello world!";
     char chars[] = "ero";

     printf("%d\n", count_chars(str, chars));

     getchar();
     return ;
 }

9.10

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>

 int palindrome( char *string )
 {
     int i, j = ;
     int len = strlen(string);
     char *strcopy = NULL;
     strcopy = malloc((len + )* sizeof(char));
     for (i = ; i < len; i++)            //将源字符串中的非字母字符去掉,并将剩下的字母转换为小写
     {
         if (isalpha(*(string + i)))
         {
             *(strcopy + j) =  tolower( *(string + i) );
             j++;
         }
     }
     *(strcopy + j) = '\0';

     len = strlen(strcopy);
     for (i = ; i < (len / ); i++)
     {
         if ( (*(strcopy + i)) != (*(strcopy + (len - i - ) ) ) )
             return ;
     }

     return ;
 }

 int main (void)
 {
     char string[] = "Madam, I'm Adam!";
     int result = ;

     result = palindrome(string);
     printf("%d\n", result);

     getchar();
     return ;
 }

9.11

 #include <stdio.h>
 #include <string.h>

 int main (void)
 {
     char input[];
     char chars[] = "the";
     int i = , count = ;
     char *pos = NULL;

     printf("Please enter some words: \n");
     scanf("%s", input);
     printf("%s\n", input);

     pos = input;
     while ((pos = strstr(pos, chars)) != NULL)
     {
         pos++;
         count++;
     }

     printf("There are %d \"%s\"!", count, chars);

     getchar();
     getchar();
     return ;
 }

9.12　　9.13　　9.14

 #include <stdio.h>
 #include <string.h>
 #include <ctype.h>

 char *init_alp(char *temp)
 {
     int i;
     char alp = 'A';

     for (i = ; i < ; i++)
     {

         *(temp + i) = alp;
         alp++;
     }
     *(temp + i) = '\0';

     return temp;
 }

 int prepare_key( char *key )                        //生成key
 {
     int i = , j = , k = ;
     char alp[];
     char *temp = alp;

     char *p = NULL; 

     if (key == NULL)                                        //key为空，退出
         return ;

     for (i = ; *(key + i) != '\0'; i++)
         if (!(isalpha(*(key + i))))                    //key中含有非字母字符，退出）
             return ;

     for (i = ; *(key + i) != '\0'; i++)
     {
         if (*(key + i) != ' ')                                //删除所有的空格
         {
             for (j = i + ; *(key + j) != '\0'; j++)        //将重复的字母赋值为空格
             {
                 if ( *(key + i) == *(key + j) )
                     *(key + j) = ' ';
             }
             *(key + k) = toupper(*(key + i));
             k++;
         }
     }
     *(key + k) = '\0';

     temp = init_alp(temp);                                //初始化为大写字母表
     p = temp;
     while ((p = (strpbrk(p, key))) != NULL)                //将字母表中含有key中的字母设置为空格
     {
         *p = ' ';
         p++;
     }

     for (i = , k = ; *(temp + i) != '\0'; i++)        //删除所有的空格
     {
         if (*(temp + i) != ' ')
         {
             *(temp + k) = *(temp + i);
             k++;
         }
     }
     *(temp + k) = '\0';

     key = strcat(key, temp);

     return ;
 }

 void encrypt( char *data, char const *key )            //给数据加密
 {
     int i, state;
     char temp[];
     char *init = NULL;
     char *p = NULL;
     char chg;

     init = init_alp(temp);

     for (i = ; *(data + i) != '\0'; i++)
     {
         if (isalpha(*(data + i)))
         {
             if (isupper(*(data + i)))
                 state = ;
             else
             {
                 *(data + i) = toupper(*(data + i));
                 state = ;
             }
             p = strchr(init, *(data + i));
             chg = *(key + (p - init));
             *(data + i) = state ? chg : tolower(chg);
         }
     }
 }

 void decrypt( char *data, char const *key )            //给数据解密
 {
     int i, state;
     char temp[];
     char *init = NULL;
     char *p = NULL;
     char chg;

     init = init_alp(temp);

     for (i = ; *(data + i) != '\0'; i++)
     {
         if (isalpha(*(data + i)))
         {
             if (isupper(*(data + i)))
                 state = ;
             else
             {
                 *(data + i) = toupper(*(data + i));
                 state = ;
             }
             p = strchr(key, *(data + i));
             chg = *(init + (p - key));
             *(data + i) = state ? chg : tolower(chg);
         }
     }
 }

 int main (void)
 {
     char key[] = "Hellomnnnnab";
     char temp[];
     char *key_m = temp;
     char data[] = "Hello world!";

     key_m = init_alp(key_m);
     printf("%s\n", key);                //显示输入的key

     if (prepare_key(key))
     {
         printf("\nAlpha: \n");            //显示大写字母表
         printf("%s\n", key_m);
         printf("\nKey: \n");            //显示生成的key秘钥
         printf("%s\n", key);

         printf("\nEncode: \n");
         printf("%s\n", data);
         encrypt(data, key);                //加密
         printf("%s\n", data);            

         printf("\nDecode: \n");
         printf("%s\n", data);
         decrypt(data, key);                //解密
         printf("%s\n", data);
     }
     else
         printf("Key error!\n");

     getchar();
     return ;
 }

9.15

 #include <stdio.h>
 #include <string.h>
 #include <ctype.h>

 void dollars(char *dest, char const *src)
 {
     int i, j, srclen = , offset = , state = ;
     int a = , b = ;
     char *destbak = NULL;
     destbak = dest;

         srclen = strlen(src);
         *dest++ = '$';

     if (srclen >= )
     {
         a = (srclen - ) / ;
         b = (srclen - ) % ;

         for (i = ; (i < a); i++)
         {
             if ( i ==  )
             {
                 for (j = ; j < b; j++)
                 {
                     *(dest++) = *(src++);
                 }
             }

             if (b != )
                 *(dest++) = ',';

             for (j = ; j < ; j++)
                 *(dest++) = *(src++);
         }

         if ((a == ) && (b != ))
         {
             for (j = ; j < b; j++)
             {
                 *(dest++) = *(src++);
             }
         }
         *((dest++)) = '.';

         for ( ; *(src) != '\0';dest++, src++)
             *(dest) = *(src);
         *(dest) = '\0';
     }
     else
     {
         memset(dest, '', );
         *(++dest) = '.';
         dest++;
         for (i = ; i <  - srclen; i++)
             *(dest++) = '';

         for (i = ; i < srclen; i++)
             *(dest + i) = *(src + i);
     }
 }

 int dollchk(char *src)                            //检查要处理的数据中是否有非数字字符
 {
     int i;
     for (i = ; *(src + i) != '\0'; i++)
     {
         if (!isdigit(*(src + i)))
         {
             return ;
         }
     }
     return ;
 }

 int main (void)
 {
     char temp[] = {  };                //目标缓存
     char dollar[];
     char *dest = temp;
     int state = ;

     printf("Please enter some numbers: \n");
     scanf("%s", dollar);

     state = dollchk(dollar);
     if (!state)                            //检查要处理的数据中含有非数字字符，报错，退出
     {
         printf("Data error!\n");
         getchar();
         getchar();
         return ;
     }

     printf("%s\n", dest);
     printf("%s\n", dollar);

     dollars(dest, dollar);
     if (*dest != '\0')
         printf("%s\n", dest);

     getchar();
     getchar();
     return ;
 }

9.16

 #include <stdio.h>
 #include <string.h>

 int format( char *format_string, char const *digit_string )
 {
     int formatlen = strlen(format_string);
     int digitlen = strlen(digit_string);
     int i, j, k;
     char *p = NULL;

     if (formatlen < digitlen)
         return ;
     if ((*digit_string) == '\0')
         return ;

     if ((p = strchr(format_string, '.')) != NULL)
     {
         if ((k = formatlen - (p - format_string)) > digitlen)
         {
             for (i = formatlen, j = digitlen; j >= ; i--, j--, k--)
             {
                 *(format_string + i) = *(digit_string + j);
             }

             for (; k > ; i--, k--)
             {
                 *(format_string + i) = '';
             }

             if ( (*(format_string + i) == '.') )
             {
                 i--;
                 *(format_string + i) = '';
             }

             for (i--; i >= ; i--)
             {
                 *(format_string + i) = ' ';
             }
         }
         else
         {
             for (i = formatlen, j = digitlen; j >= ; i--, j--)
             {
                 if ( (*(format_string + i) == ',')
                     || (*(format_string + i) == '.') )
                     i--;
                 *(format_string + i) = *(digit_string + j);
             }
             for (; i >= ; i--)
                 *(format_string + i) = ' ';
         }
     }

     return ;
 }

 int main (void)
 {
     char formats[] = "###,###.#####";
     char const digits[] = "";

     printf("%s\n", formats);
     printf("%s\n", digits);
     if (format(formats, digits))
         printf("%s\n", formats);
     else
         printf("Data error!\n");

     getchar();
     return ;
 }

9.17