Использовать события:
#include <SFML/Graphics.hpp>
int main()
{
// Create the main window
sf::RenderWindow window(sf::VideoMode(800, 600), "SFML window");
int count = 0;
while (window.IsOpened())
{
sf::Event event;
while (window.GetEvent(event))
{
if (event.Type == sf::Event::Closed)
window.Close();
if (event.Type == sf::Event::KeyPressed && event.Key.Code == sf::Key::A)
++count;
}
window.Clear();
// Do whatever you want with count.
window.Display();
}
return 0;
}