What does it mean when the first “for” parameter is blank?

Question

I have been looking through some code and I have seen several examples where the first element of a for cycle is omitted.

An example:

for ( ; hole*2          


        

Answer 1

Suppose you wanted to

for (hole=1 ; hole*2 <= currentSize; hole = child)

But the value of hole just before the for loop was already 1, then you can slip this initilization part of the loop:

/* value of hole now is 1.*/
for ( ; hole*2 <= currentSize; hole = child)