Array Defualts

Okay ive tried a bunch of ways… some were really dumb.
Q. How do I set the width of the array and length and set each of the values in it to the same number.
This is for a game im working on. (Tile like you could of guessed.)
Note: I know you use for loops to find the x and y of the values… This doesnt work, but think its how it suppose to work. (or im horribly off in either way plz help fix)

 _global.ymap = 4;
_global.xmap = 4;
for (y=0; y<_global.ymap; y++) {
for (x=0; x<_global.xmap; x++) {[y][x] = 1;