javascript - Switch with random not working -

this current jscript code:

(modified still doesn't work)

function changebg(){     document.getelementbyid('imgbox').src = switch(eval(rand())){                                                  case 1: "img/img3.jpg";                                                          break;                                                 case 2: "img/img2.jpg";                                                          break;                                                 case 3: "img/img3.jpg";                                                          break;                                                 case 4: "img/img4.jpg";                                                          break;                                                  case 5: "img/img5.jpg";                                                          break;                                                  default: "img/background.jpg";                                                          break;                                                 }  }  function rand(){     return (math.ceil((math.random()*10)/2)); } 

my html:

<input id="bgchange" type="button" onclick="changebg()" value=">"/> 

if this:

document.getelementbyid('imgbox').src = "img/img1.jpg"; 

it works: click on button, image changes, no problem. fact want image change random 1 between 5 each time button clicked; wanted use switch works random choice inside it.

what wrong coding?! :( (i cant use jquery or anything, pure javascript, html , css, thats professor said @ least)

thank <3

https://developer.mozilla.org/en-us/docs/web/javascript/reference/statements/switch

the switch-statement "executes" strings ("img/imgx.jpg") instead of returning them, may want put switch in function , do

case 1: return "img/img3.jpg"; ... 

and keep in mind each case of switch statement must terminated break, otherwise following case-blocks executed well!