Manipulate[
 With[{ans = Integrate[func, {x, x1, x2}]}, 
  Show[Graphics[
    Plot[func, {x, -2, 2}, 
     PlotLabel -> 
      Style[Framed[Row[{"Area = ", NumberForm[ans, {2, 4}]}]], 
       If[ans > 0, RGBColor[1, .47, 0], RGBColor[.12, .61, .78]], 12, 
       "Label"] ]], 
   Graphics[
    If[x1 == x2, {}, 
     Plot[func, {x, x1, x2}, Filling -> 0 , 
      FillingStyle -> 
       If[ans > 0, RGBColor[1, .47, 0], RGBColor[.12, .61, .78]]]]], 
   ImageSize -> {350, 350}]], {{x1 , 0, "x1"}, -2, 2, 
  Appearance -> "Labeled"}, {{x2, 1, "x2"}, -2, 2, 
  Appearance -> "Labeled"} , {{func , f1, 
   "curve"} , {f1 -> "constant line", f2 -> "sine wave", 
   f3 -> "parabola"}, ControlType -> SetterBar}, 
 SaveDefinitions -> True ]