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# Dry Run an Algorithm

1. I seriously dont understand this, my teacher has gone over it but i still cant get the suss of it. Could anyone help explain how these work?

This is the sort of question related to them that i've found on past papers:

2. it basically means to run the code through in your head and fill in the trace table to show how the variables change.

left arrow means "is assigned to"
3. Thanks iainmacn, it makes sense now , sort of :P
4. That is pretty damn complicated. I can't imagine how I would manage to do that in the pressure of an exam. Usually they're a lot simpler than that.
5. take it a piece at a time, and don't get too bogged down in tracing individual steps. Try to get an idea in your head of what each loop is doing first.

ptr <-- ptr + 1

So - basically move up the array from 1 until you find a value less than the value of the variable new.

onto the second loop

values[last+1] <-- values[last]

shifts the value one slot down the array

so - move values[3] into values[4] (last is 3 at the start)

now take one off last, so it's 2

move values[2] into values[3]

keep doing that until last matches ptr

overwrite the value in values[ptr] with the contents of variable new

What it's basically doing is inserting a new value into the array at the correct position. The top loop finds the position, the second loop shuffles stuff down the array to make room for it, the last statement inserts the new value into the gap.

HTH
6. (Original post by falc0n)
I seriously dont understand this, my teacher has gone over it but i still cant get the suss of it. Could anyone help explain how these work?

This is the sort of question related to them that i've found on past papers:

What paper is this from?

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