Question

In linux g++ compiler, the third number is not printed, and “reached” is not printed.
But I expected that “reached” will be printed, after that it would go into infinite loop.
It executes as expected on windows using Codeblocks

#include <iostream>
int main()
{
    int a;
    for (int i = 0; i < 3; i++) {
        std::cin >> a;
        std::cout << a;
    }
    std::cout << "reached";
    while (1) {}
    return 0;
}

Answer 1

Because you are never ending the program, and thus never flushing your stdout (cout) output.

You can either change:

 cout<<"reached";

to:

 cout<<"reached" << endl;

or:

 cout<<"reached" << flush;

Or simply remove your forever loop.

Another alternative is to use cerr << "reached"; – that will be printed immediately, since cerr is not buffered.