循环语句

while循环

//在while循环中，break用于永久地终止循环
//在while循环中，continue的作用是跳过本次循环continue后面的代码，直接去判断部分，看是否进行下一次循环

while(表达式)
循环语句;

int main()
{
    int i = 1;
    while (i <= 10)
    {
        if (i == 5)
        {
            continue; //死循环
        }
        printf("%d\n", i);
        i++;
    }
}

//EOF end of file 文件结束标志
int main()
{
    int i = 0;
    while ((i = getchar()) != EOF)
    {
        putchar(i);
    }
}

for

for(exp1;exp2;exp3)
循环语句;

int main()
{
    int i = 0;
    int j = 0;
    for (i = 0;i < 3;i++)
    {
        for (j = 0;j < 3;j++)
        {
            printf("xixi\n"); //打印九次
        }
    }
}

int main()
{
    int i = 0;
    int j = 0;
    for (;i < 3;i++)
    {
        for (;j < 3;j++)
        {
            printf("xixi\n"); //打印三次
        }
    }
}

do while 循环

do
循环语句;
while(表达式);

实践练习

//二分查找

int main()
{
    int arr[10] = { 1,2,3,4,5,6,7,8,9,10 };
    int k = 7;
    int sz = sizeof(arr) / sizeof(arr[0]);
    int left = 0;
    int right = sz - 1;
    while (left <= right)
    {
        int mid = (left + right) / 2;
        if (arr[mid] > k)
        {
            right = mid - 1;
        }
        else if(arr[mid] < k)
        {
            left = mid + 1;
        }
        else
        {
            printf("找到了:%d", mid);
            break;
        }
    }
    if (left > right)
        printf("没有这个数字");
}

#include <string.h>
#include <windows.h>
int main()
{
    char arr1[] = "happy every day!!!";
    char arr2[] = "##################";
    int left = 0;
    int right = strlen(arr1) - 1;
    while (left <= right)
    {
        arr2[left] = arr1[left];
        arr2[right] = arr1[right];
        left++;
        right--;
        printf("%s\n", arr2);
        Sleep(1000); //睡眠一秒
        system("cls"); //清屏
    }
    printf("%s\n", arr2);

int main()
{
    int i = 0;
    char password[20] = { 0 };
    for (i = 0;i < 3;i++)
    {
        printf("请输入密码<:");
        scanf("%s", password);//数组名就是地址
        if (strcmp(password, "123456") == 0)
        {
            printf("密码正确");
            break;
        }
        else
        {
            printf("输入错误，重新输入\n");
        }
    }
    if (i == 3)
    {
        printf("错误三次，退出程序");
    }
}

#include <time.h>

void menu()
{
    printf("*****************************************\n");
    printf("**************   0.exit    **************\n");
    printf("**************   1.start   **************\n");
    printf("*****************************************\n");
}


void game()
{
    //随机数,取1-100的数字
    int num = rand() % 100 + 1;
    int predict = 0;
    printf("请猜一下：\n");
    while (1)
    {
        scanf("%d", &predict);
        if (predict > num)
        {
            printf("大了\n");
        }
        else if (predict < num)
        {
            printf("小了\n");
        }
        else
        {
            printf("正确！\n");
            break;
        }
    }
}

//猜数字
int main()
{
    srand((unsigned int)time(NULL));
    int cho = 0;
    do
    {

        menu();
        printf("请选择:\n");
        scanf("%d", &cho);
        switch (cho)
        {
        case 0:
            printf("游戏结束\n");
            break;
        case 1:
            game();
            break;
        default:
            printf("输入错误，请重新输入\n");
            break;
        }
    } while (cho);
}