Modulus Error

I'm having trouble with modulus giving me the wrong answer.

It's taking 734170 and dividing by 7 and is coming up with a remainder of 3, which is wrong.

Here's the bugged out code:

Code:

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// firstDayCount is set to 734190
// and dayNum is set to 21 at this point

firstDayCount = firstDayCount - (dayNum - 1) ;

firstDayCount = firstDayCount % 7;
 
// for some reason, after this line of code it comes the answer of 3 when it should be 4

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I was wondering if there is a special way modulus works that I'm not fully aware of that could be causing it to come up with this answer.

Quote:

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Originally Posted by ace10414

I'm having trouble with modulus giving me the wrong answer.
It's taking 734170 and dividing by 7 and is coming up with a remainder of 3, which is wrong.

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The code is working fine. The remainder is 3.
Your calculation that it should be 4 is wrong.

734170 = 104881*7+3

Thank you for your clarification. :)

It seems I was misunderstanding how modulus worked.

My teacher had told me that modulus would take the first digit to the right of the decimal as the remainder. Which is why I thought the answer was 4 because

734170/7 is 104881.4286

That would be correct only for (mod 10) operations.

Quote:

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Originally Posted by ace10414

Thank you for your clarification. :)

It seems I was misunderstanding how modulus worked.

My teacher had told me that modulus would take the first digit to the right of the decimal as the remainder. Which is why I thought the answer was 4 because

734170/7 is 104881.4286

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You must perform the above calculation then take the decimal expansion:

0.428571 ...

Then multiply this by what you divided by, which in this case is 7:

Which comes to 3 assuming the decimal expansion is to a great enough degree.

Thanks a lot for all the help. : D

I'm sure I can get my program to work with all of this advice.

Quote:

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Originally Posted by ace10414

Thank you for your clarification. :)

It seems I was misunderstanding how modulus worked.

My teacher had told me that modulus would take the first digit to the right of the decimal as the remainder. Which is why I thought the answer was 4 because

734170/7 is 104881.4286

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By the way, you can get the first decimal digit by doing this:
static_cast<int>((734170.0/7.0)*10.0)%10 = 4

(make sure you are using floating point calculation for everything inside the cast)

Oh, sweet! I'll use that instead since modulus works different than I had anticipated. Thanks!