程序代码：

#include <fstream>
#include<iostream>
int main( )
{
    using namespace std;
    ifstream in_stream;
    ofstream out_stream;
    in_stream.open("infile.you");
    out_stream.open("outfile.you");
    int first, second, third;
    in_stream >> first >> second >> third;
    out_stream << "The sum of the first 3\n"
               << "numbers in infile.you\n"
               << "is " << (first + second + third)
               << endl;
    in_stream.close( );
    out_stream.close( );
system("pause");
    return 0;
}