Why won't this tween the textlabel smoothly?

[Moolah101]

case WM_COMMAND:
if(LOWORD(wParam) == 1){
DestroyWindow(button);
for(float a=20; a<50; a=a+.5){
MoveWindow(textfield, a, 20, 100, 20, TRUE);
Sleep(100);
}
}
break;


just trying to tween it smoothly to the right

and its not doing it smoothly at all..help? (also im new so i hope this is the correct place D: )