Write a program that calculates sum of the integers numbers
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What is the product if the question is write a program that calculates and prints the sum of the even integers from 2 to 30?
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Antworten (5)
Florin Neacsu
am 11 Apr. 2011
2+4+6+...+30=2(1+2+3+...+15)=2*(15*16)/2=15*16
So 2+4+...+n = floor(n/2)*(floor(n/2)+1).
Regards, Florin
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Matt Fig
am 11 Apr. 2011
The product would be the sum of the even integers from 2 to 30 ;-).
Seriously, what have you tried so far on this homework problem?
2 Kommentare
Paulo Silva
am 11 Apr. 2011
I hate when it takes more time to understand what people want than to make their answer!
Paulo Silva
am 11 Apr. 2011
v=2:30;
sum(v(~mod(v,2)))
3 Kommentare
Image Analyst
am 15 Aug. 2017
mod(v, 2) will be either 0 or 1. The tilde inverts that, so 0 becomes 1, and 1 becomes 0.
DGM
am 4 Mär. 2023
Importantly, using ~ implicitly casts the numeric result from mod() to logical (along with doing the inversion). Otherwise, the indexing operation would fail if the indices were numeric 0 and 1, as you'd be trying to access the zeroth element of v.
Doug Eastman
am 11 Apr. 2011
or
sum(2:2:30)
2 Kommentare
Paulo Silva
am 11 Apr. 2011
that's simple but if you change the start value from 2 to 1 you do the sum of odd numbers instead, also if the last value is 31 or some odd number the result won't be correct, unfortunately that's not very flexible code.
Paulo Silva
am 11 Apr. 2011
btw that does work and is a good answer for the question (only if the values don't change), +1 vote
Matt Tearle
am 11 Apr. 2011
disp(240)
Or, for pedants who claim that evaluation is not the same as calculation,
disp(239+1)
1 Kommentar
Sean de Wolski
am 11 Apr. 2011
This is definitely the most compact and efficient way to do this. +1.
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