实验2

task1

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define N 5
#define N1 80
#define N2 35
int main() {
    int cnt;
    int random_major, random_no;
    srand(time(NULL));      
    cnt = 0;
    while (cnt < N) {
        random_major = rand() % 2;
        if (random_major) {
            random_no = rand() % N1 + 1;
            printf("20256343%04d\n", random_no);
          
        }
        else {
            random_no = rand() % N2 + 1;
            printf("20256136%04d\n", random_no);
        }
        cnt++;
    }
    return 0;
}

ans1：strand（）能生成随机数，time（NULL）可以返回当前系统时间，综上生成了一个以当前时间为种子的随机数。
ans2：生成学号。
task2

#include <stdio.h>
int main() {
    int choice, quantity;
    float total_price = 0, amount_paid, change;
    while (1) {
        printf("\n自动饮料售卖机菜单:\n");
        printf("1. 可乐 - 3元/瓶\n");
        printf("2. 雪碧 - 3 元/瓶\n");
        printf("3. 橙汁 - 5 元/瓶\n");
        printf("4. 矿泉水 - 2 元/瓶\n");
        printf("0. 退出购买流程\n");
        printf("请输入饮料编号: ");
        scanf_s("%d", &choice);
        if (choice == 0)
            break;
        if (choice < 1 || choice > 4) {
            printf("无效的饮料编号，请重新输入。\n");
            continue;
        }
        printf("请输入购买的数量: ");
        scanf_s("%d", &quantity);
        if (quantity < 0) {
            printf("购买数量不能为负数，请重新输入。\n");
            continue;
        }
        if (choice == 1 || choice == 2)
            total_price += 3 * quantity;
        else if (choice == 3)
            total_price += 5 * quantity;
        else
            total_price += 2 * quantity;
        printf("请投入金额: ");
        scanf_s("%f", &amount_paid);
        change = amount_paid - total_price;
        printf("本次购买总价: %.2f 元\n", total_price);
        printf("找零: %.2f 元\n", change);
        total_price = 0;
    }
    printf("感谢您的购买，欢迎下次光临！\n");
    return 0;
}

ans1：删去总价归零，在循环中会不断累加。
ans2：跳过当前循环的剩余部分，直接进入下一次循环的判断。

task3

#include <stdio.h>
char c;
int main(){
	while(1){	
	c = getchar();
	if(c==EOF){
	break; }
	if(c=='y')
	printf("wait a minute\n");
	else if(c=='g')
	printf("go,go,go\n");
	else if(c=='r')
	printf("stop!\n");
	else 
	printf("somthing must be wrong...\n");
	getchar();
	}
	return 0;
}

task4

#include <stdio.h>;
double sum, max=0, min=20000, a, b;
int main()
{
	printf("请输入今日开销，直到输入-1终止：\n");
	while (1) {
		scanf_s("%lf", &a);
		if (a == -1) {
			printf("今日总开销：%.1lf\n",sum);
			printf("今日最高一笔消费：%.1lf\n", max);
			printf("今日最低一笔消费：%.1lf\n", min);
			break;
		}
		else {
			sum += a;
			if (a <= min) {
				min = a;
			}
			else if (a >= max) {
				max = a;
			}
		}

	}
	return 0;
}

task5

#include <stdio.h>;
int a, b, c;
int main() {
	while(1){
		scanf_s("%d%d%d", &a, &b, &c);
		if (a + b > c && a + c > b && b + c > a) {
			if ((a == b&&a!= c )|| (a == c&& a!= b) || (b == c&&b != a)) {
				printf("等腰三角形\n");
			}
			else if (a * a + b * b == c * c || b * b + c * c == a * a || a * a + c * c == b * b) {
				printf("直角三角形\n");
			}
			else if (a == b,b == c) {
				printf("等边三角形\n");
			}
			else {
				printf("普通三角形\n");
			}

		}
		else {
			printf("不能构成三角形\n");
		}
	}
	return 0;
}

task6

#include <stdio.h>
#include <stdlib.h>
int main() {
	int lucky = rand() % 30 + 1, a;
	printf("猜猜2025年11月哪一天是你的lucky day\n");
	printf("开始喽，你有三次机会，猜吧：\n");
	for (int i = 1; i <=3; i++) {
		scanf_s("%d", &a);
		if (a == lucky) {
			printf("哇，猜中了；）");
			break;
		}
		else {
			 if (a < lucky) {
				 printf("你猜的日期早啦，你的luckyday还没到呢\n");
				 if (i == 3) {
					 printf("次数用完了，偷偷告诉你，你的luckyday是：%d", lucky);
				 }
				 else { printf("再猜：\n"); }
			}
			else if (a > lucky) {
				printf("你猜的日期晚了，你的luckyday已经过了\n");
				if (i == 3) {
					printf("次数用完了，偷偷告诉你，你的luckyday是：%d", lucky);
				}
				else	
					printf("再猜：\n");
			}
		}
	}
	return 0;