//task1

#include <stdio.h> 
#include <stdlib.h> 
#include <time.h> 
#define N 5

int main()
{
    int grade, number;
    int i;

    srand(time(0));// 以当前系统时间作为随机种子

    for (i = 0; i < N; ++i)
    {
        grade = rand() % 4 + 2018;
        number = rand() % 999 + 1;
        printf("%d8330%04d\n", grade, number);
    }

    return 0;
}

/*问题1：取2018到2021之间一个随机整数*/
/*问题2：取1到999之间一个随机整数*/
/*问题3：随机生成从2018年到2021年之间学生的学号*/

//task2

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#define N 3

int main()
{
    int i;
    int day, guess;

    srand(time(0));
    day = rand() % 30 + 1;

    printf("猜猜2022年4月哪一天会是你的lucky day？\n");
    printf("\n开始喽，你有三次机会，猜吧（1~30）:  ");

    for (i = 0; i < N; ++i)
    {
        if (i != 0)
            printf("\n再猜（1~30）:  ");

        scanf("%d", &guess);

        if (day > guess)
            printf("\n你猜的日期早了，你的lucky day还没到呢\n");
        else if (day < guess)
            printf("\n你猜的日期晚了，你的lucky day已经过啦\n");
        else
        {
            printf("\n哇，猜中了:-)\n");
            break;
        }
    }

    if (day != guess)
        printf("\n次数用完啦，偷偷告诉你：4月，你的lucky day是%d号\n", day);

    return 0;
}

//task3

#include<stdio.h>

int main()
{
    char a, b;
    while (scanf("%c%c", &a, &b) != EOF)
    {
        if (a == 'r')
            printf("stop!\n");
        else if (a == 'g')
            printf("go go go\n");
        else if (a == 'y')
            printf("wait a minute\n");
        else
            printf("something must be wrong...\n");
    }
    return 0;
}

//task4

#include<stdio.h>

int main()
{
    int n, a;
    double s, i, j;

    while (scanf("%d%d", &n, &a) != EOF)
    {
        getchar();
        s = 0;
        j = 0;
        for (i = 1; i <= n; ++i)
        {
            j = j * 10 + a;
            s += i / j;
        }
        printf("n = %d, a = %d, s = %f\n\n", n, a, s);
    }
    return 0;
}

//task5

#include<stdio.h>

int main()
{
    int line, column, s;
    for (line = 1; line <= 9; ++line)
    {
        for (column = 1; column <= line; ++column)
        {
            s = column * line;
            printf("%d*%d = %2d ", column, line, s);
        }
        printf("\n");
    }
    return 0;
}

//task6_1

#include<stdio.h>

int main()
{
    int n, i;
    printf("Input n:");
    scanf("%d", &n);
    for (i = 1; i <= n; i++)
    {
        printf(" O \n");
        printf("<H>\n");
        printf("I I\n\n");
    }
    return 0;
}

//task6_2

#include<stdio.h>

int main()
{
    int n, i;

    printf("Input n:");
    scanf_s("%d", &n);

    for (i = 1; i <= n; i++)
    {
        printf(" O    ");
    }
    printf("\n");

    for (i = 1; i <= n; i++)
    {
        printf("<H>   ");
    }
    printf("\n");

    for (i = 1; i <= n; i++)
    {
        printf("I I   ");
    }

    return 0;
}

//task6_3

#include<stdio.h>

int main()
{
    int n, m, i, j;

    printf("Input n:");
    scanf_s("%d", &n);

    for (j = 1; j <= n; j++)
    {
        m = 2 * (n - j) + 1;
        for (i = 1; i <= j - 1; i++)
        {
            printf("      ");
        }
        for (i = 1; i <= m; i++)
        {
            printf(" O    ");
        }
        printf("\n");

        for (i = 1; i <= j - 1; i++)
        {
            printf("      ");
        }
        for (i = 1; i <= m; i++)
        {
            printf("<H>   ");
        }
        printf("\n");

        for (i = 1; i <= j - 1; i++)
        {
            printf("      ");
        }
        for (i = 1; i <= m; i++)
        {
            printf("I I   ");
        }
        printf("\n");
    }
    return 0;
}

实验总结：

1.随机数的设置与使用，循环的嵌套。

2.注意回车计为一个输入项时对循环造成的影响，用getchar()可吸收。