How does a WHILE loop work in GML?

Answer 1

The while loop works as follows:

{
while( [expression is true] ) {
//Do this code
}
}

The while loop re-runs until the expression contained within the parentheses is false. Take a look at this example:

{
while(!place_meeting(x,y,obj_ground)) {
y += 1;
}
}

This while loop tells the object to move down one pixel until it collides with obj_ground. Unfortunately, nothing guarantees that this loop will not run forever. Always make sure that when you construct a while loop that you make sure that it does not run forever. Take a look at this whileloop:

{
while(obj_ball.y < y) {
draw_sprite(sprite_index,0,x,y);
}
}

This while loop will run for ever. Why? It does not have any statements that insure that the while loop aborts. Again, Always make sure that when you construct a loop that you put statements in the loop that will eventually abort the loop. y -= 1; is the statement in this new while loop that eventually aborts the loop:

{
while(obj_ball.y < y) {
draw_sprite(sprite_index,0,x,y); y -= 1;
}
}