struct point p; #p就是一个结构变量
p.x = 12;
p.y = 20;

案例一：使用结构体

//
//  main.c
//  structure
//
//  Created by liuxinming on 15/4/12.
//  Copyright (c) 2015年 liuxinming. All rights reserved.
//

#include <stdio.h>

//声明结构类型
struct date{
    int month;
    int day;
    int year;
};


int main(int argc, const char * argv[]) {
    
    //结构变量&使用
    struct date today;
    today.month = 04;
    today.day = 12;
    today.year = 2015;
    
    printf("Today is date is  %i-%i-%i.\n",today.year, today.month, today.day);
    
    
    return 0;
}

//
//  main.c
//  structure
//
//  Created by liuxinming on 15/4/12.
//  Copyright (c) 2015年 liuxinming. All rights reserved.
//

#include <stdio.h>
#include <stdbool.h>

//声明结构类型
struct date{
    int month;
    int day;
    int year;
};

bool isLeap(struct date d);//判断是否为闰年
int numberOfDays(struct date d);


int main(int argc, const char * argv[]) {
    
    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] = {31,28,31,30,31,30,31,31,30,31,30,31};
    
    if(d.month == 2 && isLeap(d)){
        days = 29;//闰年
    } 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;
}

Enter today's date(mm dd yyyy):12 31 2014
Tomorrow's date is 2015-1-1.
Program ended with exit code: 0

指向结构的指针

struct date {
  int month;
  int day;
  int year;
} myday;

struct date *p = &myday;

(*p).month = 12;
p->month = 12;

//
//  main.c
//  structure
//
//  Created by liuxinming on 15/4/12.
//  Copyright (c) 2015年 liuxinming. All rights reserved.
//

#include <stdio.h>

struct point {
    int x;
    int y;
};

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


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

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

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

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

10
50
10, 50
10, 50

结构数组

struct date dates[100];

struct date dates[] = {
 {4,5,2005},
 {2,4,2005}
};

//
//  main.c
//  structure
//
//  Created by liuxinming on 15/4/12.
//  Copyright (c) 2015年 liuxinming. All rights reserved.
//

#include <stdio.h>

struct time{
    int hour;
    int minutes;
    int seconds;
};

struct time timeUpdate(struct time now);


int main(void) {
   
    struct time testTime[5] = {
        {11,59,59},
        {12,0,0},
        {1,29,29},
        {23,59,59},
        {19,12,27}
    };
    int i;
    
    for (i = 0; i < 5; i++) {
        printf("Time is %.2i:%.2i:%.2i\n", testTime[i].hour,testTime[i].minutes, testTime[i].seconds);
        
        testTime[i] = timeUpdate(testTime[i]);
        
        printf("... one second later it's %.2i:%.2i:%.2i\n", testTime[i].hour,testTime[i].minutes, testTime[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;
}

Time is 11:59:59
... one second later it's 12:00:00
Time is 12:00:00
... one second later it's 12:00:01
Time is 01:29:29
... one second later it's 01:29:30
Time is 23:59:59
... one second later it's 00:00:00
Time is 19:12:27
... one second later it's 19:12:28
Program ended with exit code: 0

struct dateAndTime{
  struct date sdate;
  struct time stime;
}

struct rectangle{
    struct point pt1;
    struct point pt2;
};

    //如果有变量
    struct rectangle r;
    //就可以有：
    r.pt1.x = 1;
    r.pt1.y = 2;
    r.pt2.x = 11;
    r.pt2.y = 22;
    
    //如果有变量定义
    struct rectangle *rp;
    rp = &r;
    //那么这四种形式是等价的
    //r.pt1.x , rp->pt1.x, (r.pt1).x, (rp->pt1).x
    //但是没有rp->pt1->x 因为pt1不是指针