C学习笔记-小程序（长期更新）

产生随机数

int t = (int)time(NULL);
srand(t);
int num = rand() % 10;

利用keybd_event函数自动打印,mouse_event函数保存文件

#include <Windows.h>

void data(char str);

int main()
{
	WinExec("notepad",SW_MAXIMIZE);
	for (int i = 0x30; i < 0x3A; i++)
	{
		printf("i = %d", i);
		data(i);
		Sleep(1000);
	}
	SetCursorPos(10, 30); //指定鼠标光标位置
	mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);
	mouse_event(MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
	Sleep(1000);
	SetCursorPos(10, 200);
	mouse_event(MOUSEEVENTF_LEFTDOWN, 0, 0, 0, 0);
	mouse_event(MOUSEEVENTF_LEFTUP, 0, 0, 0, 0);
	Sleep(1000);

	data(VK_RETURN);
	Sleep(1000);

	data(0x30);
	Sleep(1000);
	data(VK_RETURN);
	Sleep(1000);
	return 0;
}

void data(char str)
{
	keybd_event(str, 0, 0, 0);
	keybd_event(str, 0, 2, 0);
}

实现小数转整数的四舍五入功能

double f = 2.65;
int result = f + 0.5;
printf("四舍五入后的值为：%d\n", result);

查找数组中第二大值

int array[10] = { 23, 44, 21, 65, 87, 7, 33, 89, 57, 93};
int max
int smax;
max = array[0] > array[1] ? array[0] : array[1];
max = array[0] > array[1] ? array[1] : array[0];
for (int i = 2; i < 10; i++)
{
	if (max < array[i])
	{
		smax = max;
		max = array[i];
	} else if ((max > array[i]) && (smax < array[i]))
	{
		smax = array[i];
	}
}
printf("smax = %d\n", smax);

幂函数的实现（以2为例）

int getPow(int n)
{
    if (n == 0)
        return 1;
    int val = 2;
    for (int i = 0; i < n; i++)
        val *= 2;
    return val;
}

十进制转二进制

void to_binary(unsigned int n)
{
	unsigned int i = n % 2;
	if (n >= 2)
		to_binary(n / 2);
	printf("%c", i + 0x30);
}

正整数n以内的素数和

此程序有很多地方可以优化

int sum(int n)
{
	if (n == 2)
		return 2;
	else
	{
		if (isprime(n, 2))
			return n + sum2(n - 1);
		else
			return sum2(n - 1);
	}
}

int isprime(int n, int key) //判断你是否为素数，是返回1，不是返回0
{
	if (n < 2)
		return 0;
	if (n == key)
		return 1;
	if (n % key == 0)
		return 0;
	else
		return isprime(n, key + 1);
}
```

### 实现字符串拷贝函数strcpy
```c
void strcpy(char *dest, const char *src)
{
    while(*dest++ = *src++);
}
```

### 实现字符串拷贝函数strncpy
```c
void strncpy(char *dest, const char *src,int n)
{
    while((*dest++ = *src++) && (n--));
    *(dest - 1) = 0;
}
```

### 实现文件拷贝
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *args[])
{
	if (argc < 3)
	{
		return 0;
	}
	FILE *p1 = fopen(args[1], "rb");
	FILE *p2 = fopen(args[2], "wb");
	if ((p1 == NULL) || (p2 == NULL))
	{
		return 0;
	}

    char buf[1024] = { 0 };
	while (!feof(p1))
	{
		size_t size = fread(buf, 1, sizeof(buf), p1);//由于fread与feof的差异造成fread到结尾与feof不同
		fwrite(buf, 1, size, p2);//从fread读了多少字节出来，就往fwrite写多少个字节
	}
	fclose(p1);
	fclose(p2);
	return 0;
}
```

### windows和linux都可用的代码
在gcc编译时候添加参数`-DLINUX`，以下代码就可在不改变源代码情况下，同时在windows和linux下编译通过
```c
#include <stdio.h>

#ifdef LINUX
#include <unistd.h>
#else
#include <Windows.h>
#endif

int main()
{
    while(1)
    {
        printf("a\n");
#ifdef LINUX
        sleep(1);
#else
        Sleep(1000);
#endif
    }
    return 0;
}
```

### 两头堵模型
1. 初始化条件
2. strstr strchr
3. 让指针重新初始化
```c
void main()
{
	char *p = "     abcd     ";
	int ncount = 0;
	int i, j;
	i = 0;
	j = strlen(p) -1;
	while (isspace(p[i]) && p[i] != '\0')
	{
		i++;
	}
	while (isspace(p[j]) && j>0 )
	{
		j--;
	}
	ncount = j - i + 1;
	printf("ncount:%d \n", ncount);
}
```