import java.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner s=new Scanner(System.in);
        int n=s.nextInt();
        float S=0;
        for(int i=0;i<n;i++){
            float score=s.nextFloat();
            S+=score;
        }
        s.close();
        System.out.printf("%.1f",S);
    }
}

答案必须固定是一位小数

#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    int n;
    cin>>n;
    float score,S=0.0;
    for(int i=0;i<n;i++){
        cin>>score;
        S+=score;
    }
    cout<<fixed<<setprecision(1)<<S<<endl;
    return 0;
}

#include<iostream>
using namespace std;
int main()
{
    int n;cin>>n;
    float *a;
    a=new float [n];
    float sum=0;
    for(int i=0;i<n;i++) cin>>a[i];
    for(int i=0;i<n;i++) sum+=a[i];
    printf("%.1f",sum);
    return 0;
}