C语言九阴真经

#define Area 1000  
struct student{
char *last_name;
int student_id;
char grade;
int a;
};

#include <stdio.h> 
#include "f.h"
#define PI 3.1415926
#define LIMIT 20
struct employee_data
{
int a;
};


int main(void)
{
//引用
printf("%d\n",Area);

//字符
char c;
c='A';
int age;
char first,end;
printf("%c\n",c);
printf("%3c\n",c);
printf("%3c\n",'A');
//scanf("%d",&age);
//printf("%d\n",age);
//scanf("%c",&first);
//printf("%c\n",first);

char *p1;
p1=&c;
printf("%c%d%c\n",*p1,*p1+1,*p1+2);
//printf("%c",'\a');//响铃
//char d=getchar();//putchar()
//printf("%c\n",d);

const int p_sea=20;
//p_sea=30;会报错，向只读变量赋值
float x,y;
x=2.0;
y=3.0;
printf("%f\n",x*y);
printf("%f\n",PI);
double d1=1.123456789;
printf("%lf\n",d1);

int i=1,sum=0;
while (i<7){
sum=sum+i;
i++;
}
printf("%d\n",sum);

int sz[3]={23,15,78};
sz[1]=2;
printf("%d\n",sz[1]);

//求数组长度
int count=sizeof(sz)/sizeof(int);  
printf("%d\n",count);

typedef int myint;
myint i1=9;
printf("%d\n",i1);
printf("%d\n",sizeof(i1));//输出4 int是4位

//指针和数组关系
int sz1[4]={40,82,67,11};
int *p;
p=sz1;
printf("*p %d\n",*p);//40
printf("*p+1 %d\n",*p+1);//41
printf("*p+2 %d\n",*p+2);//42

printf("*p %d\n",*p);//40
printf("*p+1 %d\n",*(p+1));//82
printf("*p+2 %d\n",*(p+2));//67

struct card{
int pips;
char suit;
}c1,c2;
c1.pips=3;
c1.suit='5';
c2=c1;
printf("struct c2.pips: %d\n",c2.pips);

typedef struct{
int re;
int im;
}complex;
complex as,ac[2];
as.re=89;
ac[0].re=1;
ac[1].re=2;
printf("struct ac[0].re: %d\n",ac[0].re);
printf("struct ac[1].re: %d\n",ac[1].re);
printf("struct ac[0].re: %d\n",ac[0].re);

struct student tmp;
tmp.last_name="Canada";
tmp.grade='A';
tmp.student_id=122;
tmp.a=0;
printf("struct tmp.last_name: %s\n",tmp.last_name);

struct employee_data e1;
e1.a=12;
int e11=getdata(e1);
printf("struct e11: %d\n",e11);

int e12=getdata_add(&e1);
printf("struct e12: %d\n",e12);

//与或非
int y1=3;
int y2=0;
int y3=y1&y2;
printf("y3 &: %d\n",y3);
printf("-9 >>31: %d\n",abs(-9));

#undef __FD_SETSIZE
#define __FD_SETSIZE    1024
printf("#define: %d\n",__FD_SETSIZE);

return 0;
}

//一个负数右移31位后会变成 0xffffffff，一个正数右移31位则为 0x00000000
//0xffffffff ^ a + a = - 1
//因为 1011 ^ 1111 = 0100 异或1111其实是把a的0和1进行了颠倒。
int abs(int x)
{
    return (x ^ (x >> 31)) - (x >> 31);
}

int getdata(struct employee_data e)
{
return e.a;
}
int getdata_add(struct employee_data *e)
{
return e->a;
}