var n,i,s:longint; begin write('nhap so n=');readln(n); s:=0; for i:=1 to n do s:=s+i; writeln(' tong n so nguyen la:',s); readln; end.
Câu 1:
#include <bits/stdc++.h>
using namespace std;
long long n,i,s;
int main()
{
cin>>n;
s=0;
for (i=1; i<=n; i++) s+=i;
cout<<s;
return 0;
}