PTA-C入门与进阶练习 72|73|75

这三道练习均是输出一串数列的和，难度不大



思路
使用循环控制语句即可，第三题采用了一个factorial函数，用以求任意数的阶乘

状态
ACCEPTED

代码

72

#include <stdio.h>

int main(int argc, char **argv) {
	int n;
	scanf("%d",&n);
	double sum =0.0;
	int i =1;
	for(i;i<=n;i++){
		sum += 1.0/(2*i-1);
	}
	printf("sum = %lf",sum);
	return 0;
}

73

#include <stdio.h>

int main(int argc, char **argv) {
	double sum = 0;//initialize holder for sum
	int i = 0; //initialize loop controller
	int flag = 0;//initalize the controller for add/sub
	int n;
	scanf("%d",&n);
	for(i;i<n;i++){
		if(flag){
			sum-=1.0/(1+3*i);
			flag = 0;
		} else{
			sum+=1.0/(1+3*i);
			flag = 1;
		}
	}
	printf("%.3lf",sum);
	return 0;
}

75

#include <stdio.h>
int factorial(int num);

int main(int argc, char **argv) {
	int n = 0;
	int i = 1;
	int sum = 0;
	
	scanf("%d",&n);
	for(i;i<=n;i++){
		//printf("factorial(%d)=%d\n",i,factorial(i));
		sum += factorial(i);
	}
	printf("%d",sum);
	return 0;
}

int factorial(int num){
	int rst = 1;
	int i = 1;
	for(i;i<=num;i++){
		rst = rst*i;
	}
	return rst;
}

Note
输出控制的时候注意使用 %lf 来输出浮点数，不然会造成错误。