C语言学习(12)

 1 #include <stdio.h>
 2 
 3 //定义一个宏
 4 #define PI 3.14
 5 #define N  88
 6 #define PATH  "/mnt/hgfs/share"
 7 
 8 int main()
 9 {
10     int r=5;
11     printf("%f\n",PI);
12     printf("%d\n",N);
13     printf("%s\n",PATH);
14     printf("%f\n",PI*r*r);
15 }

 1 #include <stdio.h>
 2 
 3 //定义一个宏函数
 4 #define ADD(a,b) a+b
 5 int myadd(int a,int b)
 6 {
 7     return a+b;
 8 }
 9 int main()
10 {
11     int m=12;
12     int n=13;
13     printf("m+n is:%d\n",ADD(m,n)); //迷惑初学者，跟函数调用类似(错误理解，宏函数不是真正的函数)
14     printf("m+n is:%d\n",myadd(m,n)); 
15 }

 1 #include <stdio.h>
 2 
 3 #define CMP(a,b) if(a>b) printf("a>b\n");\
 4 else printf("a<=b\n")
 5     
 6 int main()
 7 {
 8     int m=78;
 9     int n=76;
10     CMP(m,n);
11 }

 1 #include <stdio.h>
 2 
 3 int main()
 4 {
 5     int n1,n2;
 6     int ret;
 7     int ret1;
 8 label:
 9     printf("请输入1个整数!\n");
10     ret=scanf("%d",&n1);  //hello\n
11     //判断返回值
12     if(ret!=1)  //你输入的不是整数
13     {
14         //清除掉io缓冲区中错误的字符
15         while(getchar()!='\n');
16         goto label;
17     }
18     else
19         printf("n1 is:%d\n",n1);
20 }

1 #include <stdio.h>
2 
3 int main()
4 {
5     printf("hello world");  //液晶屏上没有输出
6     //printf("hello world\n");  //输出了
7     
8     while(1);  //不让程序退出
9 }

 1 #include <stdio.h>
 2 #include <string.h>
 3 struct student
 4 {
 5     char name[10];
 6     int age;
 7 };
 8 int main()
 9 {
10     //一个班级10个学生
11     struct student array[10];
12     strcpy(array[0].name,"张三");;
13     array[0].age=18;
14     
15     strcpy(array[1].name,"李四");;
16     array[1].age=18;
17     
18     struct student *p=array;  //&array[0]
19     printf("p->name is:%s\n",p->name);
20     printf("p->age is:%d\n",p->age);
21     
22     p++;  //跳到下一个结构体
23     
24     printf("p->name is:%s\n",p->name);
25     printf("p->age is:%d\n",p->age);
26     
27     
28 }

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <stdlib.h>
 4 //定义一个结构体
 5 struct student
 6 {
 7     char name[10];
 8     int age;  
 9 };
10 
11 int main()
12 {
13     //写法一：定义结构体变量并初始化
14     struct student stu1={"张三",18};  //int a;
15     //普通结构体采用小数点引用成员
16     printf("学生姓名：%s\n",stu1.name);
17     printf("学生年龄: %d\n",stu1.age);
18     
19     //写法二：定义结构体变量没有立马初始化，后面才赋值
20     struct student stu2;
21     //stu2.name="张三";  //数组赋值只能用strcpy()
22     strcpy(stu2.name,"李四");
23     stu2.age=18;
24   
25     //写法三：linux内核代码中很常见
26     //优点：可以不按照结构体定义的顺序赋值
27     struct student stu3={
28          .age=19,
29          .name="王五" //小数点一定要写上
30     };
31     
32     
33     //写法四：定义结构体指针
34     struct student *stu4=malloc(sizeof(struct student)); //野指针  Segmentation fault (core dumped)
35     strcpy(stu4->name,"赵六");
36     stu4->age=18;
37     printf("学生姓名：%s\n",stu4->name); 
38     printf("学生年龄: %d\n",stu4->age);
39     
40     //写法五：定义结构体指针
41     struct student *stu5=malloc(sizeof(struct student));
42     strcpy((*stu5).name,"赵七");
43     (*stu5).age=18;  
44    
45    free(stu4);
46    free(stu5);
47 }

 1 #include <stdio.h>
 2 union yy  //1<8    1字节对齐
 3 {
 4     char a;  //1
 5     char b;  //1
 6 };
 7 
 8 union tt  
 9 {
10     char a;  
11     int b;  
12 };
13 
14 union uu  //  16字节
15 {
16     char a[11];  //11
17     double b;  //8
18     int c;
19 };
20 
21 int main()
22 {
23     //定义联合体变量
24     union yy y1;
25     y1.a='@';  //只给a赋值了，b没有赋值
26     y1.b='#'; //由于a和b共用同一块内存，b覆盖掉前面a的值
27     
28     printf("sizeof yy is:%lu\n",sizeof(union yy)); //1
29     printf("sizeof tt is:%lu\n",sizeof(union tt)); //4
30     printf("sizeof uu is:%lu\n",sizeof(union uu)); //16
31     union tt t1;
32     t1.b=567;
33     //请问t1.a是多少？？？？  %d打印
34     printf("t1.a is:%c   ASCII is:%d\n",t1.a,t1.a);
35     printf("y1.a is:%c\n",y1.a);
36     printf("y1.a is:%p\n",&(y1.a));
37     printf("y1.b is:%c\n",y1.b);
38     printf("y1.b is:%p\n",&(y1.b));
39 }

 1 #include <stdio.h>
 2 
 3 //enum day {mon,tues,wen};  //默认情况下三个枚举变量值：分别是 0  1  2
 4 
 5 //enum day {mon,tues=7,wen}; // 0  7  8
 6 enum color {red,green,blue,yellow,black};
 7    //0  1  2 3 4 5 6 一个星期的七天 可读性差
 8 enum day {mon,tues=7,wen,tir,fri=2,sat}; // 0 7 8 9 2 3
 9 
10 struct car  //小汽车
11 {
12     char name[10]; //品牌
13     enum color carcolor; //车的颜色
14     float price;
15 };
16 int main()
17 {
18     //定义一台车
19     struct car car1={"奔驰s600",black,2000000.0};
20     
21     printf("mon is:%d\n",mon);
22     printf("tues is:%d\n",tues);
23     printf("wen is:%d\n",wen);
24     printf("tir is:%d\n",tir);
25     printf("fri is:%d\n",fri);
26     printf("sat is:%d\n",sat);
27 }