It's the scope. As soon as your (loop) body ends, the variables value is not guaranteed to be valid anymore. So in the next iteration of the loop, the value is again undefined and you have to initialize it again.
action super_thing()
{
while(1)
{ // Boop is "allocated" here
var Boop; // Boop is undefined here
Boop+=1*time_step; // add something to an undefined value will result in an undefined value
} // Boop is "invalidated" here
}
If you want to change a variable over multiple operations (like in the code example), you
need to do this:
action super_thing()
{ // Boop is "allocated" here
var Boop = 0; // Boop is defined here
while(1)
{
Boop+=1*time_step; // add something iteratively to the initially defined value
}
} // Boop is "invalidated" here
