I have three pushbuttons where only one can be pushed at a time and want to set a variable for this. How?
If you can only have one button pushed at a time, you can only end up with at most one of the if statements evaluate to true. In your code, you check button 2 and 3, even if button 1 is pressed. Your code can be a bit faster if you do this:
if(digitalRead(1) == 1)                       
{
  Variable = 1;            
}
else if(digitalRead(2) == 1)                       
{
  Variable = 2;              
}
else if(digitalRead(3) == 1)                       
{
  Variable = 3;  
}