c++中在键盘上输入是个正整数求其和，若输入负数终止

break的
#include <iostream>

using namespace std;

void main()
{
int a;
int sum = 0;

while(1)
{
cin >> a;
if(a >= 0)
{
sum += a;
}
else
{
break;
}
}

cout <<"sum"<<sum<<endl;
}

没有break的
#include <iostream>

using namespace std;

void main()
{
int a;
int sum = 0;

cin >> a;
while(a >=0)
{
sum += a;

cin >> a;
}

cout <<"sum"<<sum<<endl;
}

int n=0,i;
while(cin>>i&&i>=0)
{
n+=i;
}
cout<<n<<endl;
...........................................
int n=0,i;
while(cin>>i)
{
if(i<0) break;
else n+=i;
}
cout<<n<<endl;