C语言入门——结构

#include
int main()
{
	struct date {
		int month;
		int day;
		int year;
	};
	struct date today;

	today.day =6;
	today.month = 8;
	today.year = 2022;

	printf("%i年%i月%i日。n", today.year, today.month, today. day);

	return 0;
}

函数内部申明的结构类型只能在函数内部使用

• p1和p2都是point里有x和y的值

struct point{
	int x;
	int y;
};
struct point p1,p2;

• p1和p2都是一种无名结构，里面有x和y`

struct{
	int x;
	int y;
}p1,p2;

• p1和p2都是point里有x和y的值

struct point{
	int x;
	int y;
}p1,p3;

第一和第三种都声明了结构point，第二种形式没有声明point，知识定义了两个变量。

#include
int main()
{
	struct date {
		int year;
		int month;
		int day;
	};
	struct date today = { 2022,8,06 };
	struct date thismonth = { .year = 2022,.month = 8 };
	printf("%i年%i月%i日。n", today.year, today.month, today. day);
	printf("%i年%i月%i日。n",thismonth.year, thismonth.month,
	       thismonth.day);

	return 0;
}

• 结构类似与数组
• 数组用[ ]运算符和下标访问其成员
• 结构用 . 运算符和名字访问其成员

• 要访问整个结构，直接用结构变量的名字；

• 对于整个结构，可以做赋值，取地址，也可以传递给函数参数
  p1=(struct point){5,10};//相当于p1.x=5;p1.y=10;

• p1=p2;//相当于p1.x=p2.x;p1.y=p2.y;

#include
int main()
{
	struct date {
		int year;
		int month;
		int day;
	};
	struct date today ;
	today = (struct date){ 2022,8,06 };

	struct date day;
	day = today;
	printf("%i年%i月%i日。n", today.year, today.month, today. day);
	printf("%i年%i月%i日。n",day.year, day.month, day.day);

	return 0;
}

• 结构变量的名字并不是结构变量的地址，必须使用&运算符
• struct date *point=&today;

结构作为函数参数

int numberOfDays(struct date d)

• 整个结构可以作为参数的值传入函数
• 这个时候是在函数内新建一个结构变量，并复制调用者的结构的值
• 也可以返回一个结构

#include
#include

struct date {
	int month;
	int day;
	int year;
};
bool isLeap(struct date d);
int numberOfDays(struct date d);

int main()
{
	struct date today, tomorrow;

	printf("Enter today's date(mm dd yyyy):");
	scanf("%i %i %i", &today.month, &today.day, &today.year);

	if (today.day != numberOfDays(today)) {
		tomorrow.day = today.day + 1;
		tomorrow.month = today.month;
		tomorrow.year = today.year;
	}
	else if (today.month == 12) {
		tomorrow.day = 1;
		tomorrow.month = 1;
		tomorrow.year = today.year+1;
	}
	else {
		tomorrow.day = 1;
		tomorrow.month = today.month+1;
		tomorrow.year = today.year;
	}

	printf("Tomorrow's date is %i-%i-%i.n", tomorrow.year, tomorrow.month, tomorrow.day);
	return 0;
}

int numberOfDays(struct date d)
{
	int days;
	const int daysPerMonth[12] = { 31,28,31,30,31,30,31,31,30,31,30,12 };
	if (d.month == 2 && isLeap(d))
		days = 29;
	else
		days = daysPerMonth[d.month - 1];

	return days;
}

bool isLeap(struct date d)
{
	bool leap = false;

	if ((d.year % 4 == 0 && d.year % 100 != 0) || d.year % 400 == 0)
		leap = true;

	return leap;
}

#include

struct point {
	int x;
	int y;
};

struct point getStruct(void);
void output(struct point);

int main(int argc, char const* argv[])
{
	struct point y = { 0,0 };
	getStruct(y);
	y=getStruct();
	output(y);
}

struct point getStruct(struct point p)
{
	struct point p;
	scanf("%d", &p.x);
	scanf("%d", &p.y);
	printf("%d,%dn", p.x, p.y);
	return p;
}

void output(struct point p)
{
	printf("%d,%d", p.x, p.y);
}

C语言传递的是值，因此要送回读入的值只能通过赋值，输出为0，0

#include

struct point {
	int x;
	int y;
};

struct point* getStruct(struct point* p);
void output(struct point);
void print(const struct point* p);

int main(int argc, char const* argv[])
{
	struct point y = { 0,0 };
	getStruct(&y);
	output(y);
	output(*getStruct(&y));
	print(getStruct(&y));
}

struct point* getStruct(struct point* p)
{
	scanf("%d", &p->x);
	scanf("%d", &p->y);
	printf("%d,%dn", p->x, p->y);
	return p;
}

void output(struct point p)
{
	printf("%d,%d", p.x, p.y);
}
void print(const struct point* p)
{
	printf("%d,%d", p->x, p->y);
}

用->表示指针所指的结构变量中的成员

struct time testTimes[5] = {
{11,59,59},{12,0,0},{1,29,59},{23,59,59},{19,12,27}
};

#include

struct time {
	int hour;
	int minutes;
	int seconds;
};
struct time timeUpdate(struct time now);

int main(void)
{
	struct time testTimes[5] = {
		{11,59,59},{12,0,0},{1,29,59},{23,59,59},{19,12,27}
	};
	int i;

	for (i = 0;i < 5;++i) {
		printf("Time is %.2i:%.2i:%.2in",
			testTimes[i].hour, testTimes[i].minutes, testTimes[i].seconds);
		
		testTimes[i] = timeUpdate(testTimes[i]);
		printf("One seconds later is: %.2i:%.2i:%.2in",
			testTimes[i].hour, testTimes[i].minutes, testTimes[i].seconds);
	}
	return 0;
}
struct time timeUpdate(struct time now)
{
	++now.seconds;
	if (now.seconds == 60) {
		now.seconds = 0;
		++now.minutes;

		if (now.minutes == 60) {
			now.minutes = 0;
			++now.hour;

			if (now.hour == 24) {
				now.hour = 0;
			}
		}
	}
	return now;
}

• C语言提供了一个叫做typedef的功能来声明一个已有的数据类型的新名字。比如：
  typedef int Length；
  使得Length成为int类型的别名
• 这样，Length这个名字就可以代替int出现在变量定义和参数声明的地方了
  Length a,b,len;
  Length number[];
• Typedef声明新的类型的名字：
• • 新的名字是某种类型的别名
• • 改善了程序的可读性

typedef long int64_t;       //重载已有的类型名字，新名字的含义更清晰；具有可移植性
typedef struct ADate{
	int month;
	int day;
	int tear;
}Date;

int64_t i=1000000000000;
Date d={9,1,2005};