How to make an "if( variable1 < X more or less Y)"?

Okay, so I'm currently creating a little game, and I need to create a condition. In maths, it would look like something like this :

if(a < X with x included in [b -10; b +10]) 
{
    then c = 2
}

Is there an easy way to do this ?

I know it may not be really clear, so ask me further details if you didn't understand.

Sorry for my broken english I do my best.