实验2

任务1

#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));      // 以当前系统时间作为随机种子
    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;
}

结果:每次运行结果不同.
1.去掉srand(time(NULL));后:

多次运行结果相同,都为上图结果.可推测该语句作用:释放之前取得的种子.

2.该程序的功能是随机抽取同学的学号.

任务2

#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("%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("%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("%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;
}

运行结果:

1.去掉total_price = 0; 后,上次得到的总价不会清零,而是进入下一次计算.运行结果:

2.continue的作用是结束当前循环,进入下一轮循环.

任务3

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

任务4

#include <stdio.h>
int main() {
	double cost;
	double sum = 0.0;
	double max=-1, min=-1;
	printf("输入今日开销,直到输入-1终止:\n");
	while (1) {
		scanf("%lf", &cost);
		if (max == -1 && min == -1) {
			max = cost;
			min = cost;
		}

		if (cost == -1)
			break;
		sum += cost;
		if (cost > max) 
			max = cost;
		if (cost < min)
			min = cost;
	}
	printf("今日累计消费总额:%.1f\n", sum);
	printf("今日最高一笔开销:%.1f\n", max);
	printf("今日最低一笔开销:%.1f\n", min);
	return 0;
}

运行结果:

任务5

#include <stdio.h>

int main() {
	int a, b, c;
	while (scanf("%d%d%d", &a, &b, &c) != EOF) {
		if (a + b <= c || a + c <= b || b + c <= a) {
			printf("不能构成三角形\n");
			continue;
		}
		if (a == b && b == c) {
			printf("等边三角形\n");
		}
		else if (a == b || b == c || a == c) {
			printf("等腰三角形\n");
		}
		else if (a * a + b * b == c * c || a * a + c * c == b * b || b * b + c * c == a * a) {
			printf("直角三角形\n");
		}
		else
			printf("普通三角形\n");
			
	}
	return 0;
}

任务6

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void)
{
    int luckyday, guess;
    srand((unsigned int)time(NULL));
    luckyday = rand() % 30 + 1;
    printf("开始喽,你有三次机会,猜吧（1~30）:");
    int i;
    for (i = 0; i < 3; i++)
    {
        scanf("%d", &guess);
        if (guess == luckyday)
        {
            printf("哇,猜中了:)\n");
            break;
        }
        else if (guess < luckyday)
        {
            printf("你猜的日期早了,你的lucky day还没到呢\n");
        }
        else 
        {
            printf("你猜的日期晚了,你的lucky day在前面哦\n");
        }
    }
    if(i==3)
        printf("次数用光啦.偷偷告诉你,你的lucky day是%d号\n",luckyday);
    
    return 0;
}