Input/Output in C++ is primarily handled through the iostream library. cin is used for input (extraction operator >>) and cout is used for output (insertion operator <<).

Essential for interacting with users and competitive programming.

• std::cout: $O(K)$ where $K$ is the number of characters.
• Fast I/O optimization: Using ios_base::sync_with_stdio(false); cin.tie(NULL); significantly speeds up I/O for large data.

cpp Standard
#include <iostream>
#include <iomanip>

int main() {
    int x;
    std::cout << "Enter a number: ";
    std::cin >> x;
    std::cout << "You entered: " << std::setw(5) << x << std::endl;
    return 0;
}

• Forgetting endl or \n to flush the buffer or move to the next line.
• Using std::cin >> string when names have spaces (use getline instead).
• Not including <iomanip> when using manipulators like setprecision.