Double summation in C++

Question

I am currently attempting to write a program in which a user enters a number (Z) to be used to calculate the summation. I've been attempting to use nested for loops, to no avail.

This is a homework assignment, so rather an idea in the right direction than a full answer if possible.

Edit: In the example a Z of 10 is used to equate to 20790, which has been my method of checking if my code works

for(int x = 0; x<=z; x++)
{
    for(int y =0; y<=x+1; y++)
    {
        sum = (z/2)*((x^2)+y+1);
        total += sum;
    }
}

This was my last attempt, albeit a poor one.

well, this is a nested for loop problem by definition, so please send us what you tried and we can tell you where you need to fix it. — MPops, Jul 31 '18 at 16:56
I've tried different structuring, my latest one has been added — Eendjie, Jul 31 '18 at 16:58
I've also attempted solving the sum of y first to use it as a multiplier when solving for x. — Eendjie, Jul 31 '18 at 17:02
Everything was initialized as an int at the start, without values assigned. — Eendjie, Jul 31 '18 at 17:11
Possible duplicate of [Why is my power operator (^) not working?](https://stackoverflow.com/questions/4843304/why-is-my-power-operator-not-working) — phuclv, Aug 01 '18 at 02:44

score 4 · Accepted Answer · answered Jul 31 '18 at 17:04

4

First of all: did you initialize your total to 0?
Furthermore, the operator ^ does not raise to a power. It's a bitwise XOR. Simply use x*x.

answered Jul 31 '18 at 17:04

Robert Kock

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Thank you, we just moved over from python, so after seeing x**2 no longer worked I looked up the command, must've misread it. – Eendjie Jul 31 '18 at 17:06
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Just for interests sake, what would happen if total was not initialised to zero, just created with "int total;" at the start? – Eendjie Jul 31 '18 at 17:09
`total` would have an arbitrary value. It would mess up the final result. – Robert Kock Jul 31 '18 at 17:11
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I understand, thank you very much for taking the time to help with such a stupid mistake. – Eendjie Jul 31 '18 at 17:12
1

@Eendjie A slight correction: What happens if you do not initialize `total` depends on how and where you define `total`. If it is defined inside a function and not declared `static` (An Automatic or local variable) then what Robert says is correct. Its value will be undefined and likely whatever old value happened to be in the memory now used by `total`. As a static variable `total` would be zeroed for you. [Look up Storage Duration](https://en.cppreference.com/w/cpp/language/storage_duration) for more info. – user4581301 Jul 31 '18 at 18:32

Double summation in C++

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