BenHem gave me a basic algorithm like the one below for moving back and forth between boundaries. The slight problem I have is that the value actually goes beyond the boundaries. Of course one can state nominal boundaries that are slightly less, but that also means that one cannot start with the actual boundary value, since the value will never get back within the boundaries. Is there a simple solution to this?

float dir=1;
float maxValue = 99; // specify one less than needed
float minValue = 1; // specify one more than needed
float value = 1; // must start with nominal min
float incr = 1;

void draw() {
 if ((value > (maxValue)) || (value < (minValue))) {
   dir = -dir;
 }
 value += incr * dir;
 println(value);
}

PhilLo's suggestion will work in this example because your increment value is 1...but if it were larger, and you still needed to absolutely protect the value from exceeding those bounds, you would need to reverse "dir" not:
"if the value is already beyond the boundaries"
but:
"if what the value is about to become is beyond the boundaries"

so (if value + dir * incr <= boundary) ....

--Ben