float vs double

[Royceybaby]

A possibly stupid question, but I don't understand.

Take this piece of code:

float poo1( 0.1 );
poo1 = poo1 - 0.1;
 
double poo2( 0.1 );
poo2 = poo2 - 0.1;
 
QMessageBox::information( 0, "Help", QString("Float : %1\nDouble : %2").arg( poo1 ).arg( poo2 ) );

float poo1( 0.1 );
poo1 = poo1 - 0.1;
  
double poo2( 0.1 );
poo2 = poo2 - 0.1;
  
QMessageBox::information( 0, "Help", QString("Float : %1\nDouble : %2").arg( poo1 ).arg( poo2 ) );

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poo1 will return 1.49012e-09
poo2 will return 0

Why is that? Shouldn't they both be zero?

Thanks,
Royce