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?
回答（5 个）
Florin Neacsu
2011-4-11
2 个投票
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
Matt Fig
2011-4-11
1 个投票
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 个评论
Sean de Wolski
2011-4-11
You might need some bubble wrap for that.
Paulo Silva
2011-4-11
I hate when it takes more time to understand what people want than to make their answer!
Paulo Silva
2011-4-11
v=2:30;
sum(v(~mod(v,2)))
3 个评论
Brother_Devil
2017-8-15
Hi Paulo, this works fine but what is operator ~ doing here? Its hard to understand what exactly is happening after ~. I am new to coding.
Image Analyst
2017-8-15
mod(v, 2) will be either 0 or 1. The tilde inverts that, so 0 becomes 1, and 1 becomes 0.
DGM
2023-3-4
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
2011-4-11
or
sum(2:2:30)
2 个评论
Paulo Silva
2011-4-11
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
2011-4-11
btw that does work and is a good answer for the question (only if the values don't change), +1 vote
Matt Tearle
2011-4-11
disp(240)
Or, for pedants who claim that evaluation is not the same as calculation,
disp(239+1)
1 个评论
Sean de Wolski
2011-4-11
This is definitely the most compact and efficient way to do this. +1.
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