C++ incorrect output summing multiples [Solved]

Question

Passes some tests in Code Coach but not all.
/*
You need to calculate the sum of all the multiples of 3 or 5 below a given number.

Task:
Given an integer number, output the sum of all the multiples of 3 and 5 below that number.
If a number is a multiple of both, 3 and 5, it should appear in the sum only once.

Input Format:
An integer.

Output Format:
An integer, representing the sum of all the multiples of 3 and 5 below the given input.

Sample Input:
10

Sample Output:
23
*/

#include <iostream>
using namespace std;

int main() {
int sum = 0;
int x = 1;
int y;
cin >> y;
while(x<=y){
if((x % 5 == 0) != (x %3 == 0)) {
sum += x;
}
x += 1;
}
cout<<sum<<endl;
return 0;
}

If 100 is entered output is 2103 but should be 2318. Can anyone point out the error?

Answer 1

You are including y. But asked to find below the numbers of y. See my next point. x < y
!= means not equal to
|| is OR logical operator, either one or both, must be true => true

Answer 2

What is the != means there?
Should not be || there instead?
also below number y so use x<y , instead of x<=y

Answer 3

Jayakrishna🇮🇳

Interesting!

My logic was that it states :

" If a number is a multiple of both, 3 and 5, it should appear in the sum only once. "

!= appears to work in some cases but not all. I thought "as long as %5 != %3 then sum them. But now I think that maybe it adds neither to the sum if they are != ...

Could that be the problem?

What is interesting is that I tried using || instead and the output was 2418 instead of 2318. So || instead of != seems to almost work.

I can perhaps cheat by then using "sum2 = sum - y" but would still like to find the error in my logic.
https://code.sololearn.com/cXMBxX63tBnV/?ref=app

Answer 4

Jayakrishna🇮🇳

Perfect! So I now see the two errors in my logic. Thank you for your help.

Answer 5

Jayakrishna🇮🇳

I should have put 2 + 2 together... If y was 100 and my output was over by 100, I should have seen that 😶

Answer 6

can you please show your solved code