《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 = 0;
    char strarray[N+1]; //= "Hello world!    \t3I'm here!";
    char *input = strarray;
    char ch;
    unsigned int cont = 0;
    int ctr=0, spc=0, num=0, low=0, upp=0, puc=0, upr=0;
    float ctrf=0, spcf=0, numf=0, lowf=0, uppf=0, pucf=0, uprf=0;

    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*100 , spcf*100, numf*100);
    printf("lower = %.3f%%\nupper = %.3f%%\npunct = %.3f%%\n", lowf*100, uppf*100, pucf*100);
    printf("uprnt = %.3f%%\n", uprf*100);

    getchar();
    return 0;
}

 

 

9.3

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

void my_strcpy(char *dst, char *src)
{
    size_t len = 0, dstlen = 0, srclen = 0;
    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[6] = "Hello";
    char src[10] = "I'm here!";
    char *dstp = dst;
    char *srcp = src;

    my_strcpy(dstp, srcp);

    show_string(dstp);
    show_string(srcp);

    getchar();
    return 0;
}

 

 

9.4

 

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

#define  M  12
#define  N  16

void my_strcat(char *dst, char *src)
{
    size_t len = 0, dstlen = 0, srclen = 0, restlen = 0;
    dstlen = strlen(dst);
    srclen = strlen(src);
    
    len = ( (restlen = M - dstlen - 1) > 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 0;
}

 

 

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 = 0, dstlen = 0, srclen = 0, restlen = 0;
    dstlen = strlen(dest);
    srclen = strlen(src);
    
    len = ( (restlen = dest_len - dstlen - 1) > 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 0;
}

 

 

9.6

 

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

char *my_strcpy_end(char *dst, char *src)
{
    int i, dstlen = 0, srclen = 0;
    
    dstlen = strlen(dst);
    srclen = strlen(src);

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

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

int main (void)
{
    char *p = NULL;
    char dst[] = "Hello world";
    //char src[] = "123456789";
    char src[] = "123456789123456789";

    p = my_strcpy_end(dst, src);

    printf("%c\n", *(p - 1));

    getchar();
    return 0;
}

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 = 0; i < which; i++)
    {
        if ( i != 0)
            p++;
        p = strchr(p, ch);
    }

    return p;
}

int main (void)
{
    int i;
    char str[] = "Hello world!";
    int chr = 'l';
    int which = 2;

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

    for (i = -1; i < 2; i++)
        printf("%c\t", *(find + i));
    putchar('\n');

    getchar();
    return 0;
}

 

9.9

 

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

int count_chars(char const *str, char const *chars)
{
    int count = 0, len = 0;
    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 0;
}

 

 

9.10

 

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

int palindrome( char *string )
{
    int i, j = 0;
    int len = strlen(string);
    char *strcopy = NULL;
    strcopy = malloc((len + 1)* sizeof(char));
    for (i = 0; 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 = 0; i < (len / 2); i++)
    {
        if ( (*(strcopy + i)) != (*(strcopy + (len - i - 1) ) ) )
            return 0;
    }

    return 1;
}

int main (void)
{
    char string[] = "Madam, I'm Adam!";
    int result = 0;

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

    getchar();
    return 0;
}

 

 

9.11

 

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

int main (void)
{
    char input[101];
    char chars[] = "the";
    int i = 0, count = 0;
    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 0;
}

 

 

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 = 0; i < 26; i++)
    {
        
        *(temp + i) = alp;
        alp++;
    }
    *(temp + i) = '\0';

    return temp;
}

int prepare_key( char *key )                        //生成key
{
    int i = 0, j = 0, k = 0;
    char alp[27];
    char *temp = alp;
    
    char *p = NULL; 

    if (key == NULL)                                        //key为空，退出
        return 0;

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

    for (i = 0; *(key + i) != '\0'; i++)
    {
        if (*(key + i) != ' ')                                //删除所有的空格
        {
            for (j = i + 1; *(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 = 0, k = 0; *(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 1;
}

void encrypt( char *data, char const *key )            //给数据加密
{
    int i, state;
    char temp[27];
    char *init = NULL;
    char *p = NULL;
    char chg;

    init = init_alp(temp);
    
    for (i = 0; *(data + i) != '\0'; i++)
    {
        if (isalpha(*(data + i)))
        {
            if (isupper(*(data + i)))
                state = 1;
            else
            {
                *(data + i) = toupper(*(data + i));
                state = 0;
            }
            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[27];
    char *init = NULL;
    char *p = NULL;
    char chg;

    init = init_alp(temp);
    
    for (i = 0; *(data + i) != '\0'; i++)
    {
        if (isalpha(*(data + i)))
        {
            if (isupper(*(data + i)))
                state = 1;
            else
            {
                *(data + i) = toupper(*(data + i));
                state = 0;
            }
            p = strchr(key, *(data + i));
            chg = *(init + (p - key));
            *(data + i) = state ? chg : tolower(chg);
        }
    }
}

int main (void)
{
    char key[28] = "Hellomnnnnab";
    char temp[28];
    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 0;
}

9.15

 

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

void dollars(char *dest, char const *src)
{
    int i, j, srclen = 0, offset = 0, state = 0;
    int a = 0, b = 0;
    char *destbak = NULL;
    destbak = dest;

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

    if (srclen >= 3)
    {
        a = (srclen - 2) / 3;
        b = (srclen - 2) % 3;

        for (i = 0; (i < a); i++)
        {
            if ( i == 0 )
            {
                for (j = 0; j < b; j++)
                {
                    *(dest++) = *(src++);
                }
            }

            if (b != 0)
                *(dest++) = ',';

            for (j = 0; j < 3; j++)
                *(dest++) = *(src++);
        }

        if ((a == 0) && (b != 0))
        {
            for (j = 0; j < b; j++)
            {
                *(dest++) = *(src++);
            }
        }
        *((dest++)) = '.';
        
        for ( ; *(src) != '\0';dest++, src++)
            *(dest) = *(src);
        *(dest) = '\0';
    }
    else
    {
        memset(dest, '0', 4);
        *(++dest) = '.';
        dest++;
        for (i = 0; i < 2 - srclen; i++)
            *(dest++) = '0';

        for (i = 0; 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 = 0; *(src + i) != '\0'; i++)                
    {
        if (!isdigit(*(src + i)))
        {
            return 0;
        }
    }
    return 1;
}

int main (void)
{
    char temp[20] = { 0 };                //目标缓存
    char dollar[20];
    char *dest = temp;
    int state = 0;

    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 0;
    }

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

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

    getchar();
    getchar();
    return 0;
}

 

 

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 0;
    if ((*digit_string) == '\0')
        return 0;

    if ((p = strchr(format_string, '.')) != NULL)
    {
        if ((k = formatlen - (p - format_string)) > digitlen)
        {
            for (i = formatlen, j = digitlen; j >= 0; i--, j--, k--)
            {
                *(format_string + i) = *(digit_string + j);
            }

            for (; k > 0; i--, k--)
            {
                *(format_string + i) = '0';
            }

            if ( (*(format_string + i) == '.') )
            {
                i--;
                *(format_string + i) = '0';
            }

            for (i--; i >= 0; i--)
            {
                *(format_string + i) = ' ';
            }
        }
        else
        {
            for (i = formatlen, j = digitlen; j >= 0; i--, j--)
            {
                if ( (*(format_string + i) == ',') 
                    || (*(format_string + i) == '.') )
                    i--;
                *(format_string + i) = *(digit_string + j); 
            }
            for (; i >= 0; i--)
                *(format_string + i) = ' ';
        }
    }

    return 1;
}

int main (void)
{
    char formats[] = "###,###.#####";
    char const digits[] = "123";

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

    getchar();
    return 0;
}

 

 

9.17