easy if statement

How could I design an if statement to where it would return an error message if the user did not enter the values 1-31.

Like so:

PHP Code:

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cout << "Please enter the desired day (choose from 1-31) ";
    cin >> dayNum;
    if(dayNum!=1 && dayNum!=2 &&dayNum !=3 &&...)// need to make this more simple!!!!!
    {
cout << "Invalid entry\n" << endl;
        menu(proceed);
    }

    cout << "You are correct sir!\n" << endl; 


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Code:

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if( dayNum<1 || dayNum>31 )
{
    cout <<  "Error Tastic!"
}

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thanks, its almost 3 AM here, my brain is a little fried

no problem