aBgPic = new Array(11);
for(x=0; x<11; x++){
aBgPic[x] = "bg_pics/bg_pic" + x + ".jpg";
}
Specifying the length of the array in the constructor arguments (Array(11)) is possible, but not required, because arrays in AS are dynamic unlike arrays in C++. You can add elements and remove elements at will. Therefore, if you just create an empty array and use the for loop to write to elements 0 to 10, the array will extend to fit the 11 elements.
or if you are deliberately making index11 of aBgPic an array
aBgPic = ;
aBgPic[11] = ;
for (x=0; x<=11; x++) {
aBgPic[11] = “bg_pics/bg_pic”+x+“.jpg”;
}