C语言指针详解（三）

#include <stdio.h>
int add(int a, int b)
{
	return a + b;
}
int sub(int a, int b)
{
	return a - b;
}
int mul(int a, int b)
{
	return a * b;
}
int div(int a, int b)
{
	return a / b;
}
int main()
{
	int x, y;
	int input = 1;
	int ret = 0;
	do
	{
		printf("*********************\n");
		printf("*  1: add   2: sub  *\n");
		printf("*  3: mul   4: div  *\n");
		printf("*********************\n");
		printf("请选择：");
		scanf("%d", &input);
		switch (input)
		{
		case 1:
			printf("输入操作数：");
			scanf("%d %d", &x, &y);
			ret = add(x, y);
			printf("ret = %d\n", ret);
			break;
		case 2:
			printf("输入操作数：");
			scanf("%d %d", &x, &y);
			ret = sub(x, y);
			printf("ret = %d\n", ret);
			break;
		case 3:
			printf("输入操作数：");
			scanf("%d %d", &x, &y);
			ret = mul(x, y);
			printf("ret = %d\n", ret);
			break;
		case 4:
			printf("输入操作数：");
			scanf("%d %d", &x, &y);
			ret = div(x, y);
			printf("ret = %d\n", ret);
			break;
		case 0:
			printf("退出程序\n");
			break;
		default:
			printf("选择错误\n");
			break;
		}
	} while (input);
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
//qosrt函数的使⽤者要写一个⽐较函数
int int_cmp(const void* p1, const void* p2)
{
	return (*(int*)p1 - *(int*)p2);
}
int main()
{
	int arr[] = { 1, 3, 5, 7, 9, 2, 4, 6, 8, 0 };
	int i = 0;
	qsort(arr, sizeof(arr) / sizeof(arr[0]), sizeof(int), int_cmp);
	for (i = 0; i < sizeof(arr) / sizeof(arr[0]); i++)
	{
		printf("%d ", arr[i]);
	}
	printf("\n");
	return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Stu //学⽣
{
	char name[20];//名字
	int age;//年龄
};
//打印结构体
void printstruct(struct Stu* s, size_t sz)
{
	for (int i = 0; i < sz; i++)
	{
		printf("%s %d  ", s[i].name, s[i].age);
		if (i == sz - 1)
		{
			printf("\n");
		}
	}
}
//假设按照年龄来比较
int cmp_stu_by_age(const void* e1, const void* e2)
{
	return ((struct Stu*)e1)->age - ((struct Stu*)e2)->age;
}
//strcmp - 是库函数，是专门用来比较两个字符串的大小的
//假设按照名字来比较
int cmp_stu_by_name(const void* e1, const void* e2)
{
	return strcmp(((struct Stu*)e1)->name, ((struct Stu*)e2)->name);
}
//按照年龄来排序
void test2()
{
	struct Stu s[] = { {"zhangsan", 20}, {"lisi", 30}, {"wangwu", 15} };
	int sz = sizeof(s) / sizeof(s[0]);
	qsort(s, sz, sizeof(s[0]), cmp_stu_by_age);
	printstruct(&s, sz);
}
//按照名字来排序
void test3()
{
	struct Stu s[] = { {"zhangsan", 20}, {"lisi", 30}, {"wangwu", 15} };
	int sz = sizeof(s) / sizeof(s[0]);
	qsort(s, sz, sizeof(s[0]), cmp_stu_by_name);
	printstruct(&s, sz);
}
int main()
{
	test2();
	test3();
	return 0;
}

#include <stdio.h>
int int_cmp(const void* p1, const void* p2)
{
	return (*(int*)p1 - *(int*)p2);
}
void _swap(void* p1, void* p2, int size)
{
	int i = 0;
	for (i = 0; i < size; i++)
	{
		char tmp = *((char*)p1 + i);
		*((char*)p1 + i) = *((char*)p2 + i);
		*((char*)p2 + i) = tmp;
	}
}
void bubble(void* base, int count, int size, int(*cmp)(void*, void*))
{
	int i = 0;
	int j = 0;
	for (i = 0; i < count - 1; i++)
	{
		for (j = 0; j < count - i - 1; j++)
		{
			if (cmp((char*)base + j * size, (char*)base + (j + 1) * size) > 0)
			{
				_swap((char*)base + j * size, (char*)base + (j + 1) * size, size);
			}
		}
	}
}
int main()
{
	int arr[] = { 1, 3, 5, 7, 9, 2, 4, 6, 8, 0 };
	int i = 0;
	bubble(arr, sizeof(arr) / sizeof(arr[0]), sizeof(int), int_cmp);
	for (i = 0; i < sizeof(arr) / sizeof(arr[0]); i++)
	{
		printf("%d ", arr[i]);
	}
	printf("\n");
	return 0;
}

#include <stdio.h>
int main()
{
	int a = 10;
	printf("sizeof(a)   = %d\n", sizeof(a));
	printf("sizeof a    = %d\n", sizeof a);
	printf("sizeof(int) = %d\n", sizeof(int));
	return 0;
}

#include <stdio.h>
#include <string.h>
int main()
{
	char arr1[3] = { 'a', 'b', 'c' };
	char arr2[] = "abc";
	printf("strlen(arr1) = %d\n", strlen(arr1));
	printf("strlen(arr2) = %d\n", strlen(arr2));
	printf("sizeof(arr1) = %d\n", sizeof(arr1));
	printf("sizeof(arr2) = %d\n", sizeof(arr2));
	return 0;
}