分支和循环练习

三个数从小到大输出

# include<stdio.h>
int main() {
	int a, b, c;
	scanf("%d%d%d", &a, &b, &c);
	if (a < b) {
		int temp = a;
		a = b;
		b = temp;
	}
	if (a < c) {
		int temp = a;
		a = c;
		c = temp;
	}
	if (b < c) {
		int temp = b;
		b = c;
		c = temp;
	}
	printf("%d  %d  %d\n", a, b, c);
	return 0;
}

一百以被三整除

# include<stdio.h>
int main() {
	int i;
	for (i = 0; i <= 100; i++) {
		if (i % 3 == 0) {
			printf("%d\n", i);
		}
	}
	return 0;
}

最大公约数（给两个数，求最大公约数）

辗转相除法：以除数和余数反复做除法运算，当余数为 0 时，取当前算式除数为最大公约数，

# include<stdio.h>
int main() {
	int m = 24, n = 18, r;
	while (m % n!=0) {
		r = m % n;
		m = n;
		n = r;
	}
	printf("%d\n", n);
}

打印闰年，1000年到2000年

1.能被4整除，不能被100整除

两者“或”的关系
2；能被400整除是闰年

# include<stdio.h>
int main() {
	int year = 0;
	int count = 0;
	for (year = 1000; year <= 2000; year++) {
		if (year % 4 == 0&&year%100!=0) {
			printf("%d\n", year);
			count++;
		}
		else if (year % 400 == 0) {
			printf("%d\n", year);
			count++;
		}
	}
	printf("%d\n", count);
	return 0;
}

# include<stdio.h>
int main() {
	int year;
	int count = 0;
	for (year = 1000; year <= 2000; year++) {
		if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
			printf("%d\n", year);
			count++;
		}
	}
	printf("%d\n", count);
}

100到200的素数

1：试除法 产生2到i-1

# include<stdio.h>
int main() {
	int i; 
	for (i = 100; i <= 200; i++) 
	{
//判断i是否为素数
		//1：试除法 产生2到i - 1
		int j = 0;
		for (j = 0; j < i; j++) {
			if (i % j == 0) {
				break;
			}
		}
		if (j == i) {
			printf("%d\n",i);
		}
	}
	return 0;
}

2:

i=a*b
a,b中有一个小于i的开平方

# include<stdio.h>
#include<math.h>
# include<string.h>
int main() {int i;
		for (i = 100; i <= 200; i++)
		{
			//判断i是否为素数
					//1：试除法 产生2到i - 1
			int j = 0;
			for (j = 0; j < sqrt(i); j++) {
				if (i % j == 0) {
					break;
				}
			}
			if (j >sqrt(i)) {
				printf("%d\n", i);
			}
		}
		return 0;
	}

数9的个数

数一下1到100有多少个9
99两个9，不能用else

# include<stdio.h>
int main() {
	int i;
	int count = 0;
	for (i = 1; i <= 100; i++) {
		if (i % 10 == 9) {
			count++;
		}
		 if (i / 10 == 9) {
			count++;
		}
	}
	printf("%d\n", count);
}

分数求和

# include<stdio.h>
int main() {
	int i;
	double  sum = 0;
	int flag = 1;
	for (i = 1; i <= 100; i++) {
		sum = flag*1.0/ i + sum;
		flag = -flag;
	}
	printf("%lf\n", sum);
	return 0;
}

求十个数的最大值

注意max的赋值

# include<stdio.h>
int main() {
	int arr[] = { 1,2,3,4,5,6,7,8,9,10 };
	int max = arr[1];
	int i;
	int se = sizeof(arr) / sizeof(arr[0]);
	for (i = 1; i <= se; i++) {
		if (max < arr[i]) {
			max = arr[i];
		}
	}
	printf("%d\n", max);
}

乘法口诀

# include<stdio.h>
int main() {
	int i, j,sum;
	for (i = 1; i <= 9; i++) {
		printf("\n");
		for (j = 1; j <= i; j++) {
			sum = i * j;
			printf("%d*%d=%d\t", i, j, sum);
		}
	}
}

猜数字游戏

1：电脑生成随机数
2：猜数字

# include<stdio.h>
# include<stdlib.h>
# include <time.h>
void game() {
	int guess;
	int ret = 0;
	//用时间戳来表示
	ret = rand()%100+1;
	//printf("%d\n", ret);
	while (1) {
		printf("猜数字\n");
		scanf("%d", &guess);
		if (guess > ret) {
			printf("猜大了\n");
		}
		else if (guess < ret) {
			printf("猜小了\n");
		}
		else printf("猜对了");
		break;
	}

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

int main() {
	int input = 0;
	srand((unsigned int)time(NULL));
	do {
		menu();
		printf("请选择\n");
		scanf("%d", &input);
		switch (input) {
		case(1): game();
			break;
		case(2):
			printf("退出游戏\n");
			break;
		default:
			printf("输出错误\n");
			break;
		}

	} while (input);
	return 0;
}