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 
    
     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 maxint 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```cvoid strcpy(char *dest, const char *src){
        while(*dest++ = *src++);}```### 实现字符串拷贝函数strncpy```cvoid strncpy(char *dest, const char *src,int n){
        while((*dest++ = *src++) && (n--));    *(dest - 1) = 0;}```### 实现文件拷贝```c#include 
    
     #include 
     
      #include 
      
       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 
       
        #ifdef LINUX#include 
        
         #else#include 
         
          #endifint 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 strchr3. 让指针重新初始化```cvoid 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);}```