C primer plus第14章(结构和其他数据形式)

//结构体与指针
#include <stdio.h>
#define LEN 20
//#include <console.h> //mac下需要
struct names
{
char first[LEN];
char last[LEN];
};

struct guy
{
struct names handle;
char favfood[LEN];
char job[LEN];
float income;
};
int main(void)
{
struct guy fellow[2] =
{
{   {"Ewen","Villard"},
"grilled salmon",
"personality coach",
58112.00
},
{   {"Rodney","Swillbelly"},
"tripe",
"tabloid editor",
232400.00
}
};
struct guy * him;//这是一个指向结构的指针
printf("address #1:%p #2:%p\n",&fellow[0],&fellow[1]);
//结构与数组不同，需要用取地址符（&）取地址
him = &fellow[0];//告诉该指针它要指向的地址
printf("pointer #1: %p #2:%p\n",him,him+1);
//用指针获取结构的值用->运算符
//him->income等同于fellow[0].income 等同于(*him).income
printf("him->income is $%.2f:(*him) .income is $%.2f\n",him->income,(*him).income);
him++;//指向下一个结构
printf("him->favfood is %s:him->handle.last is %s\n",him->favfood,him->handle.last);
return 0;
//如果him是指向名为barnery的结构的指针
//barney.income == (*him).income == him->income
}

//如果要在结构内声明指针而不是数组（指针只保存地址，如果声明数组则保存的是实际的值）
struct names
{
char *fname;
char *lname;
int letters;
};

void getinfo(struct namect *pst) {

char temp[81];
printf("Please enter your first name.\n");
gets(temp);
//分配用来存放值的内存（用完别忘记free）
pst->fname = (char*)malloc(strlen(temp) + 1);
//把名字复制到已分配的内存中
strcpy(pst->fname,temp);
printf("Please enter your last name.\n");
gets(temp);
//分配用来存放值的内存（用完别忘记free）
pst->lname = (char*)malloc(strlen(temp) + 1);
//把名字复制到已分配的内存中
strcpy(pst->lname,temp);
}

//伸缩型数组成员
#include <stdio.h>
#include <stdlib.h>
struct flex
{
int count;
double average;
double scores[];//伸缩型数组成员
};
void showFlex(const struct flex *p);
int main(void)
{
struct flex * pf1,*pf2;
int n = 5;
int i;
int tot = 0;
//为结构和数组分配存储空间
//为结构分配存储空间sizeof(struct flex)
//为数组分配存储空间n * sizeof(double)
pf1 = malloc(sizeof(struct flex) + n * sizeof(double));
pf1->count = n;
for(i=0; i<n; i++)
{
pf1->scores[i] = 20.0 - i;
tot += pf1->scores[i];
}
pf1->average = tot / n;
showFlex(pf1);
n= 9;
tot = 0;
pf2 = malloc(sizeof(struct flex) + n * sizeof(double));
pf2->count = n;
for(i=0; i<n; i++)
{
pf2->scores[i] = 20.0 - i/2.0;
tot += pf2->scores[i];
}
pf2->average = tot / n;
showFlex(pf2);
free(pf1);
free(pf2);
return 0;
}
void showFlex(const struct flex *p)
{
int i;
printf("Scores:");
for(i=0; i<p->count; i++)
{
printf("%g ",p->scores[i]);
}
printf("\nAverage:%g\n",p->average);
}

#include <stdio.h>
#include <stdlib.h>
#define MAXTITL 40
#define MAXAUTL 40
#define MAXBKS 10 //图书最多的本书

//建立book模板
struct book
{
char title[MAXTITL];
char author[MAXAUTL];
float value;
};

int main(void)
{
struct book library[MAXBKS];//结构数组
int count = 0;
int index,filecount;
FILE *pbooks;
int size = sizeof(struct book);
//以二进制的追加模式打开文件
if((pbooks = fopen("book.dat","a+b")) == NULL)
{
fputs("Can`t open book.dat file\n",stderr);
exit(1);
}
//定位到文件开始处
rewind(pbooks);

//读取并输出文件中已经存在的数据
while(count < MAXBKS && fread(&library[count],size,1,pbooks) == 1)
{
if(count == 0)
{
puts("Current contents of book.dat");
}
printf("%s by %s:$%.2f\n",library[count].title,library[count].author,library[count].value);
count++;
}

filecount = count;
//如果文件存储已满
if(count == MAXBKS)
{
fputs("The book.dat file is full.",stderr);
exit(2);
}

//如果文件还能存储
puts("Please add new book titles.");
puts("Press [enter] at the start of a line to stop.");
//录入新的图书
while(count <MAXBKS && gets(library[count].title) != NULL && library[count].title[0] != '\0')
{
puts("Now enter the author.");
gets(library[count].author);
puts("Now enter the value.");
//下标递增
scanf("%f",&library[count++].value);
//清空输入行
while(getchar() != '\n')
{
continue;
}
//如果未大于最大存储数量，提示输入下一本
if(count< MAXBKS)
{
puts("Enter the next title");
}
}

//写入文件
if(count > 0)
{
puts("Here is the list of your books:");
for(index = filecount; index < count; index++)
{
printf("%s by %s:$%.2f\n",library[index].title,library[index].author,library[index].value);
//count-filecount 本次写入数量（本次写入后总数-写入前总数）
fwrite(&library[filecount],size,count-filecount,pbooks);
}
}
else
{
puts("No books? Too bad.\n");
}
puts("Bye.\n");
fclose(pbooks);
return 0;
}

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

char showmenu(void);
void eatline(void);//读至行末
void show(void(*fp)(char *),char * str);
void ToUpper(char *);   //把字符串转换为大写
void ToLower(char *);   //把字符串转换为小写
void Transpose(char *);  //大小写专置
void Dummy(char *);     //不改变字符串

int main(void)
{
char line[81];
char copy[81];
char choice;
void(*pfun)(char *);//指向一个函数，该函数接受一个char*参数，并且没有返回值
puts("Enter astring(empty line to quit):");
while(gets(line) != NULL && line[0] != '\0')
{
while((choice = showmenu()) != 'n')
{
//用switch语句用来设置指针赋值不同的函数地址
switch(choice)
{
case 'u':
pfun = ToUpper;
break;
case 'l':
pfun = ToLower;
break;
case 't':
pfun = Transpose;
break;
case 'o':
pfun = Dummy;
break;
}
strcpy(copy,line);//为show（）制作一份拷贝
show(pfun,copy);//使用用户选择的函数
}
puts("Enter astring(empty line to quit):");

}
puts("Bye!");
return 0;
}

char showmenu(void)
{
char ans;
puts("Enter menu choice:");
puts("u)uppercase l)lowercase");
puts("t)transposed case o)original case");
puts("n)next string");
ans = getchar();            //获取用户的响应
ans = tolower(ans);         //转换为小写
eatline();                  //删除行中剩余部分
while(strchr("ulton",ans) == NULL)
{
puts("Please enter a u,l,t,o, or n:");
ans = tolower(getchar());
eatline();
}
return ans;
}

void eatline(void)
{
while(getchar()!= '\n')
{
continue;
}

}

void ToUpper(char * str)
{
while(*str)
{
*str = toupper(*str);
str++;
}
}

void ToLower(char * str)
{
while(*str)
{
*str = tolower(*str);
str++;
}
}

void Transpose(char * str)
{
while(*str)
{
if(islower(*str))
{
*str = toupper(*str);
}
else if(isupper(*str))
{
*str = tolower(*str);
}
str++;
}
}

void Dummy(char * str)
{
//不改变字符串
}

void show(void(*fp)(char*),char * str)
{
(*fp)(str);//把用户选择的函数作用于str
puts(str);//显示结果
}