sum of multiples of 3 from 0 to 100

Calculate the sum of all the multiples of 3 from 0 to 100 without using an if construct or vectorization.

I'm not sure how to do it without using an if construct.

sum = 0;
for x = 0:100
    if mod(x,3) == 0
        sum = sum + x;
    end
end
fprintf ('The sum is %4d \n', sum);

[David Fletcher]

You're using an if construct - the only reason you need an if construct is to filter out the numbers that you don't need. So, don't generate the useless numbers in the first place.

As a hint - you can use a step size when writing this: for x = 0:100

Answer 1

[Rik]

If I was your teacher I would just tell you to use a loop, leaving you to decide what you aren't allowed to do.

In this case you need to read the documentation for the colon function. It will tell you how you can introduce a step size.

doc colon

You should also avoid the use of sum as a variable name, as you are likely to use the sum function elsewhere in your code. If it already is a variable, that will cause strange issues.

[Walter Roberson]

I think the colon would count as vectorization.

It is then questionable whether using a colon in a for counts as vectorization. The model MATLAB uses is as if the limit expression was evaluated and all of the terms were stored ahead of time, but there is evidence that the implementation does not do that in the case of using a colon range.

Answer 2

[Manas Minnoor]

Hey Mina,

You can generate only the multiples of 3 in the for loop using the colon operator.

Please refer to the following documentation to view the different ways to utilize a for loop:

https://in.mathworks.com/help/matlab/ref/for.html

Hope this helps.

[Rik]

Please refrain from posting complete solutions to homework questions. That only encourages cheating.

Answer 3

[Walter Roberson]

s = 0;
for x = 0 : 100
  s = s + (mod(x,3) == 0).*x;
end
s

s = 1683

sum(0:3:100)

ans = 1683

[Rik]

If colon is vectorization, then you should probably replace this with a while loop.

[Walter Roberson]

Does a while loop count as an if statement ?