Re: scanf and c++

 James Kanze <>
Mon, 16 Jul 2007 07:29:20 -0000
On Jul 15, 8:33 pm, "Xavier Serrand" <> wrote:

With GCC version 3.4.4 (mingw special) , following code gives stange resu=



void encapsulation_c(void)
   double x, y;
   std::printf("Calcul de moyenne\n");
   std::printf("Entrez le premier nombre : ");
   std::scanf("%f", &x);
   std::printf("\nEntrez le deuxieme nombre : ");
   std::scanf("%f", &y);
   //y = 3;
   std::printf("\n\nLa valeur moyenne de %8.2f et de %8.2f est %8.2f\n",
      x, y, ((x+y)/2));

output is :

Calcul de moyenne
Entrez le premier nombre : 1.0

Entrez le deuxieme nombre : 2.0

La valeur moyenne de 0.00 et de 0.00 est 0.00

Some idea ?

The code has undefined behavior, so nothing can really be
considered strange.

Forget about scanf. It's very difficult to use correctly to
begin with, and very, very fragile, leading to absolutely
unmaintainable code. Something like:

    double x, y;
    std::cout << "Calcul de moyenne" << std::endl ;
    std::cout << "Entrez le premier nombre : " ;
    std::cin >> x ;
    std::cout << "\nEntrez le deuxieme nombre : " ;
    std::cin >> y ;

Does the trick nicely (except that it lacks error handling), and
is robust in face of change. (It works equally well, regardless
of whether x and y are double, float or even int.)

James Kanze (GABI Software)
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