类型别名 typedef

#include <stdio.h>

// Rust style type alias
typedef char  i8;
typedef short i16;
typedef int   i32;
typedef long  i64;

typedef unsigned char  u8;
typedef unsigned short u16;
typedef unsigned int   u32;
typedef unsigned long  u64;

typedef char* string;

int main() {
  i8 character = 'A'; // 本质就是 char
  u8 number    = 255; // 本质就是 unsigned char
  string str   = "hello world"; // 本质就是 char*

  printf("Size of i8 : %zu bytes\n", sizeof(i8));
  printf("Size of i16: %zu bytes\n", sizeof(i16));
  printf("Size of i32: %zu bytes\n", sizeof(i32));
  printf("Size of i64: %zu bytes\n", sizeof(i64));
}

枚举类型 enum

在人类的概念中, 有很多东西是有限的且不会变更的(比如:季节只有4个,一周只有7天),此时就可以使用枚举来提升代码可读性

#include <stdio.h>

// 枚举所有的值都是 int 类型
enum SEASONS {
  // 如果不指定值, 默认从0开始, 后续递增1
  SPRING,
  SUMMER,
  AUTUMN,
  WINTER
};

enum WEEK {
  // 如果指定一个值, 从指定的值开始, 后续递增1
  MONDAY = 1,
  TUESDAY,
  WEDNESDAY,
  THURSDAY,
  FRIDAY,
  SATURDAY,
  SUNDAY
};

int main() {
  enum SEASONS spring = SPRING;
  printf("SEASONS start with: %d\n", SPRING);
  printf("SPRING: %d \n", SPRING);
  printf("SUMMER: %d \n", SUMMER);
  printf("AUTUMN: %d \n", AUTUMN);
  printf("WINTER: %d \n", WINTER);

  printf("\n");

  enum WEEK monday = MONDAY;
  printf("WEEK start with: %d \n", monday);
  printf("MONDAY    : %d \n", MONDAY);
  printf("TUESDAY   : %d \n", TUESDAY);
  printf("WEDNESDAY : %d \n", WEDNESDAY);
  printf("THURSDAY  : %d \n", THURSDAY);
  printf("FRIDAY    : %d \n", FRIDAY);
  printf("SATURDAY  : %d \n", SATURDAY);
  printf("SUNDAY    : %d \n", SUNDAY);
}