help with for loops please(add 1 to 100)

[dmitrip]

hello

i am trying to write a program that will add up the first 100 positive integers and output the sum

so like 1 + 2 + 3 + 4 + 5.....all the way to 100

this is what i got soo far

[code]
var counter,total : int
counter := 1

for i :1..100
total := i + counter

put total

end for
[code]

can anybody please tell me what i can do from here

thanks alot

[neufelni]

You are making this more complicated than necessary. You don't need a counter variable, the i in the for loop acts as a counter variable. All you need is a total variable, initially set to 0. Then each time through the for loop you add the value of i to your total. Like this:

Turing:

var total : int := 0 for i :1..100     total += i end for put total

[Cervantes]

Also, note that if you pair the first number with the last, the second with the second last, the third with the third last, and so on, you can get a formula.

1 + 2 + 3 + ... + 98 + 99 + 100
= (1+100) + (2+99) + (3+98) + ... + (49+52) + (50+51)
= 101 + 101 + 101 + ... + 101 + 101 <<50 terms>>
= 101 * 50
= 101 * (100 / 2)
= n*(n+1) / 2

This is the formula that Guass developed to sum the first n natural numbers.

No need for for loops!

[Clayton]

does that formula only work with a range of natural numbers from 1 to n?

[Cervantes]

Yes. However, if you want to sum up the numbers from, say 10 to 100, you'd just sum up the numbers from 1 to 100 then subtract the numbers from 1 to 9.

[zylum]

also note that these are triangle numbers.

code:

T(1) = 1 =        * T(2) = 3 =        *                   ** T(3) = 6 =        *                   **                   *** etc...