今天练习了n项求和，统计素数求和，99乘法表

#include<stdio.h>
int main()
{
	double fz = 2;
	double fm = 1;
	int N;
	double sum = 0;
	scanf_s("%d", &N);

	for (int i = 1; i <= N; i++)
	{
		sum = sum + fz / fm;
		double temp = fz;
		fz = fz + fm;
		fm = temp;
	}
	printf("%.2lf", sum);



	return 0;
}

#include<stdio.h>
int main()
{
	int M;
	scanf_s("%d", &M);
	int N;
	scanf_s("%d", &N);
	
	int a = 0;
	int sum = 0;
	for (int i = N; i <= M; i++)
	{
		int count = 0;
		for (int j = 2; j < i; j++)
		{
			if (i % j == 0)
			{				
				count++;
				break;
			}
			/*if(count == 0)
			{
				printf("%d\n", i);						
				break;
			}
			这个判断不能放在里面，比如i=13，j=2
			i%j！=0，此时会直接运行到第二个if，因为count==0
			实际上奇数一开始和2相除，他们的余数都不为0，所以count不会++，
			导致count==0，此时会直接运行到第二个if，并break，
			所以运行程序时什么都没有
			*/
		
		
		
		}
		if (count == 0)
		{
			printf("%d\n", i);			
			a++;
			sum += i;
		}			
	}

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

		}
		printf("\n");
	}



	return 0;
}