实验2

task1

`#include <stdio.h>

include <stdlib.h>

include <time.h>

define N 5

int main() {
int 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) {
    number = rand() % 100 + 1;
    printf("20490042%04d\n", number);
}

return 0;

}`

1确保每次的随机数不同
2使输出时永远是至少4位数字
3随机生成五个学生学号

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("%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;
    }

    switch (choice) {
        case 1:
        case 2:
            total_price += 3 * quantity;
            break;
        case 3:
            total_price += 5 * quantity;
            break;
        case 4:
            total_price += 2 * quantity;
            break;
    }

    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;

}`
1 将总价变为0，便于下一次运算
2 break是终止循环 continue是进入下一个循环
3 没有必要 因为没有别的情况了

task3
`#include <stdio.h>

int main(){
int r,y,g;
char ch;

while((ch=getchar())!=EOF){
	getchar();
	switch(ch){
		case 'r':
			printf("stop!\n");
			break;
		case 'y':
			printf("wait a minute\n");
			break;
		case 'g':
			printf("go go go\n");
			break;
		default:
			printf("spmething must be wrong...\n");
			break;
	}
}

return 0;

}
`

task4
`#include <stdio.h>

int main(){
float x;
float s=0,max=0,min=20001;

printf("输入今日开销，直到输入-1终止：\n");

while(1){
	scanf("%f",&x);
	if(x==-1){
		break;
	}
	if(x>max){
		max=x;
	}
	if(x<min){
		min=x;
	}
	s+=x;
}
printf("今日累计消费总额：%.1f\n",s);
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;

}`

task5
`#include <stdio.h>

include <stdlib.h>

include <time.h>

int main(){
int day,guess,t=0;

srand(time(0));

day=rand()%30+1;

printf("猜猜2025年4月哪一天是你的lucky day\n");
printf("开始喽，你有三次机会，猜吧(1-30)：\n");

while(t<3){
	scanf("%d",&guess);
	t++;

	if(guess==day){
		printf("哇，猜中了：-）");
		return 0;
	}
	else if(guess<day){
		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在前面呢\n");
	}

	if(t<3){
		printf("再猜(1-30)：");
	}
}

printf("次数用完啦。偷偷告诉你，4月你的lucky day是%d号\n",day);

return 0;

}`

task6
`#include <stdio.h>

include <stdlib.h>

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

printf("input n：");
scanf("%d",&n);

for(i=n;i>0;i--){
	for(j=0;j<n-i;j++){
		printf("        ");
	}			
	for(j=1;j<=2*i-1;j++){
		printf(" O      ");
	}
	printf("\n");

			for(j=0;j<n-i;j++){
		printf("        ");
	}

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

			for(j=0;j<n-i;j++){
		printf("        ");
	}

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

	getchar();
	getchar();
	return 0;
}`