C 语言知识点简单介绍

1. 定义常量的两种方式
   #define AGE 30 和 const int AGE = 30;

2. 指针变量（图解）

   

3. 变量类型

   
   #include<stdio.h>
   
   int main(){
     int a = 5;               //整型变量
     float b = 1.1234567890;  //浮点数变量
     char c = 'n';            //字符变量, ''
     char *d = "abc";         //字符串变量, ""
     printf("%d\n", a);
     printf("%f\n", b);       //精确到小数点后6位
     printf("%c\n", c);
     printf("%s\n", d);
   }

4. 字符串简单操作

   
   #include<stdio.h>
   
   int main(){
     char a[] = {'h', 'e', 'l', 'l', 'o', '\0'};
     char a1[6] = {'h', 'e', 'l', 'l', 'o'};
     char b[30] = "hello";
     char c[15] = "programgirl";
     char d[15];
     strcpy(d,b);  //将第二个变量赋值给第一个变量
     printf("a=%s\na1=%s\nb=%s\nd=%s\n", a, a1, b, d);
   
     strcat(b,c);  //将第二个变量拼接在第一个变量的后面
     printf("a=%s\na1=%s\nb=%s\nd=%s\n", a, a1, b, d);
   
     printf("a-length:%d\n",strlen(a));
     printf("a1-length:%d\n",strlen(a1));
     printf("b-length:%d\n",strlen(b));
   
     /*结果
         a=hello
         a1=hello
         b=hello
         d=hello
         a=hello
         a1=hello
         b=helloprogramgirl
         d=hello
         a-length:5
         a1-length:5
         b-length:16
     */
   
     return 0;
   }

5. 结构体struct 和 typedef

   
   #include<stdio.h>
   
   //定义结构体 Person
   struct Person 
   {
     char name[50];  //名字
     int age;        //年龄
   };
   
   //定义结构体 Teams, typedef 为 Team类型取一个新名字 Team
   typedef struct Teams
   {
     char name[50];  //名字 
     int count;      //人数
   }Team;
   
   typedef int NUM;
   
   int main(){
     struct Person person;  //声明 person，类型为 Person
     strcpy(person.name, "xiaoming");
     person.age = 20;
   
     // 用 typedef 取得新名字 Team 来定义 Teams 类型的结构体 team
     Team team;
     strcpy(team.name, "teamname");
     team.count = 10;
   
     NUM a = 18;
   
     // 输出 person信息
     printf("person name:%s\n", person.name);
     printf("person age:%d\n", person.age);
   
     // 输出 team 信息
     printf("team name:%s\n", team.name);
     printf("team count:%d\n", team.count);
   
     // 输出a 的值
     printf("a:%d\n",a);
   
     /*结果
       person name:xiaoming
       person age:20
       team name:teamname
       team count:10
       a:18
     */
     return 0;
   }