What does << do in C++ with cout?

<< is the stream insertion operator — it sends ("flows") data into an output stream such as cout.

cout << "Value: " << 42 << endl;

How it works:

• cout is the standard output stream object (from <iostream>)
• << is overloaded to accept many types (strings, ints, floats…), so you don't need format specifiers
• Each << returns the stream again, which is why you can chain them in one statement

Equivalent in C:

printf("Value: %d\n", 42);

Tip: Think of << as "flows into" — data flows into the stream. (>> points the other way, pulling data out.)