我的c++代码有一条错误

1、首先，好几条语句后面没有加分号；
2、在前面应该加上using namespace std;
3、应该是#include<cstdlib> 才对；
代码如下：
#include <fstream>
#include <iostream>
#include <cstdlib>
using namespace std;

int main()
{
ifstream instream;
ofstream outstream;

instream.open("input.txt") ;
if(instream.fail())

cout<<"inputfile open fail"<<endl;
exit(1);

outstream.open("output.txt") ;

cout<<"outstream open fail."<<endl;
exit(1);

int first,second,third;
instream>>first>>second>>third;
outstream<<"total is"<<(first+second+third)<<endl;

instream.close() ;
outstream.close() ;

return 0 ;
}

C中好像没有then这个词吧

直接
if(instream.fail())
{
cout<<"inputfile open fail"<<e