求1+2+3+...+N的值

#include<iostream>
using namespace std;
int main(){
      int n,s=0;cin>>n;
      for(int i=1;i<=n;++i){
            s+=i;
      }
      cout<<s;
      return 0;
}

直接上代码！

#include<iostream> using namespace std; int n; int main(){ cin>>n; cout<<n*(n+1)/2<<endl; return 0; }

#include<bits/stdc++.h>
using namespace std;
long double q,w,e,r,t,y,u,i,o,p,d,f,g,h,j,k,l,z,x,c,v,b,n,m;
string s;
long long a[100000],as[100000],asd[100000];
int main()
{
	cin>>x;
	cout<<(x+1)*(x/2)*1.000;
    return 0;
}

`

#include<iostream>
using namespace std;
int main(){
    int a,s=0;
    cin >> a;
    for(int i=1;i<=a;i++){
        s+=i;
    }
    cout << s;
    return 0;
}