V3154. The 'a % b' expression always evaluates to 0.

A modulo operation performed on an integer type always returns 0. This happens because its right operand is represented by the value 1 (-1), which is most likely a typo.

A common pattern of this error is checking if no remainder is left after dividing a value by 2. To do this, you use the modulo operation and compare the result with 0 or 1. Making a typo at this point is easy because since you anticipate the value 1, you may accidentally divide by 1 too. For example:

if ((x % 1) == 1)
{
    ....
}

The programmer wrote the value 1 instead of 2, which will result in the 'x % 1' expression always evaluating to 0 no matter the value of 'x'. Therefore, the condition will always be false.

Fixed code:

if ((x % 2) == 1)
{
    ....
}

The following example was taken from a real-life application:

const int SyncReportFrequency = 1;
....
private void TimerOnElapsed(object sender, ElapsedEventArgs e)
{
    if (_reportId % SyncReportFrequency == 0)
    {
        WriteSyncReport();
    }
}

The 'SyncReportFrequency ' is a constant equal to 1, so regardless of the value of the '_reportId' variable, the condition of the 'if' statement will always be true.

It is either that the developer made a typo in this code or the condition is superfluous. Fixed version:

const int SyncReportFrequency = 2;
....
private void TimerOnElapsed(object sender, ElapsedEventArgs e)
{
    if (_reportId % SyncReportFrequency == 0)
    {
        WriteSyncReport();
    }
}

This diagnostic is classified as:

Was this page helpful?

Message submitted.

Your message has been sent. We will email you at

If you do not see the email in your inbox, please check if it is filtered to one of the following folders:

• Promotion
• Updates
• Spam

If you can’t find an answer to your question, fill in the form below and our developers will contact you

By clicking this button you agree to our Privacy Policy statement