Factoriel.cpp
#include <iostream.h>
//-----------------------------------------------------------------------
int main()
{
  int factoriel = 1, nombre;
  cout << "Nombre ? ";
  cin >> nombre;
  for (int i=1; i<=nombre; factoriel *= i++);
  
  // ou
  // for (int i=1; i<=nombre; i++)
  //    factoriel = factoriel * i;
  
  cout << "Le factoriel est : " << factoriel << endl;
  return 0;
}
//-----------------------------------------------------------------------
Factoriel.cpp