半夜打卡第7题

#include <bits/stdc++.h>
using namespace std;
int main()
{
    double n , s = 0;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        if (i % 2 != 0) s += 1.0 / i;
        else s -= 1.0 / i;
    }
    printf("%.4f",s);
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
int main(){
    int n;
    double sum=0;
    cin>>n;
    for(int i=1;i<=n;i++)i%2==0?sum-=1.0/i:sum+=1.0/i;
    cout<<fixed<<setprecision(4)<<sum<<endl;
    return 0;
}

浓缩就是精华

#include<bits/stdc++.h>
using namespace std;
int main()
{
    double n,ans=1;
    cin>>n;
    for (int i=2;i<=n;i++)
        if (i%2==0)
            ans-=1.0/i;
        else
            ans+=1.0/i;
    cout<<fixed<<setprecision(4)<<ans;
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin >> n;
	double s = 0;//定义小数变量代表n项的和
	//循环遍历1到n
	for(int i = 1; i <= n; i++){
		//如果i是奇数用加法，i是偶数用减法
		if(i%2 == 0){
			s -= 1.0/i;
		}
		else {
			s += 1.0/i;
		} 
		
	} cout << fixed << setprecision(4)<< s << endl;
	return 0;
}