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vapour99

Fri Sep 12, 2008 11:04 am


Adding the sum of all the numbers from 1 to 50

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A simple turing problem that i would appreciate help with:

given this question: "Print the sum of the numbers from 50 to 0"

I know that the forumla ∑(F,L)= ( L? - F? + F + L)/2
would do it but apparently this can be done in a for loop (?)

anyhow; help is much appreciated; thanks in advance!


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Insectoid

Fri Sep 12, 2008 11:18 am


RE:Adding the sum of all the numbers from 1 to 50

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Add the value of the for loop (the number of the variable you gave it) to a variable starting at zero.

Are you doing this for school? If so, ask your teacher. Things as simple as this would only take a half minute for him/her to explain.


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octopi

Fri Sep 12, 2008 11:20 am


Re: Adding the sum of all the numbers from 1 to 50

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Yes, you can do it in a for loop, but its much more efficient to use the formula method.

If your teacher's making you use a for loop for this perhaps they should find an exercise where it's absolutely required to use a for loop, otherwise all they are teaching is how to do things inefficiently.

Also I don't recognize that formula, it should be 

sum = N (First + Last) / 2

shouldn't it, so for your case it'd be  51(50) / 2 = 1275


*I don't know Turing, otherwise I'd post some Turing code for you to look at*


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Insectoid

Fri Sep 12, 2008 11:24 am


RE:Adding the sum of all the numbers from 1 to 50

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Perhaps it is just to teach how to use a for loop? Learning the commands comes first; efficiency comes later. A for loop is THE simplest way to do this (in Turing). You could also use recursion, though somebody just learning might have trouble with that. 

Anyway, with a for loop this can be done in 4 lines.


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[Gandalf]

Fri Sep 12, 2008 2:05 pm


Re: RE:Adding the sum of all the numbers from 1 to 50

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A for loop is THE simplest way to do this (in Turing).
...
Anyway, with a for loop this can be done in 4 lines.
The simplest way to do it is using the formula, it's just a simple expression that can be done in 1 line.  It may be a bit more complicated to figure out, though.

If you understand anything to do with summation though, using a for loop shouldn't be a problem at all.  You go through each number up to 50 and create increase a sum variable by that value over each iteration.


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Tony

Fri Sep 12, 2008 2:34 pm


RE:Adding the sum of all the numbers from 1 to 50

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Bonus points -- prove (by induction!) that the formula works.


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Insectoid

Fri Sep 12, 2008 3:53 pm


RE:Adding the sum of all the numbers from 1 to 50

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Touche