直接上代码，有空更新题解

#include <iostream>
#include <stdio.h>
using namespace std;

int main()
{
    double x,y;

    cin>>x;
    if(0<=x&&x<5){
        y=-x+2.5;
    }
    else if(5<=x&&x<10){
        y=2-1.5*(x-3)*(x-3);
    }
    else {
    y=x/2-1.5;
    }
    printf("%.3f",y) ;
    return 0;
}

#include <iostream>
#include <stdio.h>
using namespace std;

int main()
{
    double x,y;

    cin>>x;
    if(0<=x&&x<5){
        y=-x+2.5;
    }
    else if(5<=x&&x<10){
        y=2-1.5*(x-3)*(x-3);
    }
    else {
    y=x/2-1.5;
    }
    printf("%.3f",y) ;
    return 0;
}

#include <bits/stdc++.h>
using namespace std;
const int N=1e7+10;
const int INF=0x3f3f3f3f;
int main()
{
	double x,y;
	cin>>x;
	if(0<=x&&x<5)
	{
		y=-x+2.5;
	}
	else if(5<=x&&x<10)
	{
		y=2-1.5*(x-3)*(x-3);
	}
	else if(10<=x&&x<20)
	{
		y=x/2-1.5;
	}
	cout<<fixed<<setprecision(3)<<y;
	return 0;
}

#include <iostream> #include <iomanip> using namespace std; int main(){ double n; cin>>n; if(0<=n&&n<5) n=-n+2.5; else if(5<=n&&n<10) n=2-1.5*(n-3)*(n-3); else n=n/2-1.5; cout<<fixed<<setprecision(3)<<n<<endl; return 0; }

#include <iostream> #include <iomanip> using namespace std; int main(){ double n; cin>>n; if(0<=n&&n<5) n=-n+2.5; else if(5<=n&&n<10) n=2-1.5*(n-3)*(n-3); else n=n/2-1.5; cout<<fixed<<setprecision(3)<<n<<endl; return 0; }

#include <iostream> #include <iomanip> using namespace std; int main(){ double n; cin>>n; if(0<=n&&n<5) n=-n+2.5; else if(5<=n&&n<10) n=2-1.5*(n-3)*(n-3); else n=n/2-1.5; cout<<fixed<<setprecision(3)<<n<<endl; return 0; }

#include<bits/stdc++.h>
#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    double n;
    cin>>n;
    if(0<=n&&n<5)
        n=-n+2.5;
    else if(5<=n&&n<10)
        n=2-1.5*(n-3)*(n-3);
    else
        n=n/2-1.5;
    printf("%.3lf",n);
    return 0;
}

#include <iostream>
#include <iomanip>
using namespace std;
int main(){
    double n;
    cin>>n;
    if(0<=n&&n<5)
        n=-n+2.5;
    else if(5<=n&&n<10)
        n=2-1.5*(n-3)*(n-3);
    else
        n=n/2-1.5;
    cout<<fixed<<setprecision(3)<<n<<endl;
    return 0;
}

ggf nj