LoopBodyScopeImpliesLoopLifetime

DRAFT

Observed

Correction

Here is what's right.

The lifetime of a variable declared in a loop corresponds to one iteration only, not to all iterations of the loop.

for (int element : array) {
  int sum = 0;    // sum gets freshly initialized in each iteration
  sum += element; // here sum == 0, and we just add the current element
                  // here sum == element, always
}
// here sum doesn't exist anymore

Symptoms

How do you know your students might have this misconception?

Students with this misconception may declare an accumulator variable inside the loop body, like this:

for (int element : array) {
  int sum = 0;
  sum += element;
}

They might believe that sum gets initialized to 0 in the first iteration, that in subsequent iterations sum just gets incremented, and that after the loop, sum contains the accumulated total.