/*
* Usage: call set_image (during page load) or reset_image (after page load), 
* specifying the number (of images to choose from) and 
* prefix (the path to the image up to the sequence number). 
* Images must be sequentially numbered starting with zero.
*/

/*
* Set the image by writing to document stream as page is rendered
*/
function set_image(number,prefix) {

	// choose random image
    var image = choose_image(number,prefix);

    // write to page
    document.write(image);
}

/*
* Set the image by dynamically resetting the src of img with id 'randimg'
* after the page has loaded
*/
function reset_image(number,prefix){

	// choose random image
    var image = choose_image(number,prefix);

    // tell calling page how to set the src for randimg
    document.randimg.src = image;
}


/*
* Returns the path to the randomly selected image
*/
function choose_image(number,prefix){
    
    // total number of images to choose from, and their locations
    var image_number = number;
    var image_prefix = prefix;
    images = new Array();
    for (var i=0; i <= image_number; i++) {
        images[i] = image_prefix + i + ".jpg";
    }
    
    // create random number between 0-1
    var random_multiplier= Math.random();
    
    // to get *image_number* possible answers multiply by (image_number - 1)    
    var outcome_multiplier = image_number - 1;
    var random_number      = random_multiplier * outcome_multiplier;
    
    // we need an integer for array
    var random_int 	 = Math.round(random_number);
	var image		 = images[random_int];

	return image;
}