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natural-numbers-sum.r

REBOL [ File: %natural-numbers-sum.r Date: 26-9-2014 Title: "Natural numbers sum" Purpose: { Sums all the natural numbers up to a given input. Uses the equality: 1 + 2 + 3 +... + n = n*(n+1)/2 to avoid looping. } Author: "Caridorc" library: [ level: 'beginner platform: 'all type: [tutorial tool] domain: [math] tested-under: "Windows" support: riki100024 AT gmail DOT com license: {CC 3.0 Attribution only} see-also: none ] ] view layout [ across button "Sum of all the natural numbers up to " 400x30 font-size 20 [alert to-string ((to-integer a/text) * ((to-integer a/text) + 1) / 2)] a: field font-size 20 200x30 ]
halt ;; to terminate script if DO'ne from webpage