/*I will comment the lines with the comment above the line. For example, consider this to be the comment about the if statement*/
if(key_pressed(KEY_SPACE) and me.z==0 and jumpstuntimer.elapsed>=jumpstuntime and jumping==false)
{
//Your first issue: the 2 equal signs check for equality of an object, jumping in this case. Change this to jumping=true;
jumping==true;
p.play_stationary("sounds/jump.ogg",false);
//This is also an issue: It is inside the jumping statement, and thus, won't be triggered when jumping equals true.
if(me.z<5 and risetimer.elapsed>=risetime)
{
risetimer.restart();
me.z+=1;
}
}
/*Consider adding in a third boolean as well as another jumping timer that keeps track of how long you're gonna be in the air. If you don't, you'll continue to rise until you reach 5 and just hang there, unless you add in the if statement that checks for the equality of player's z coordinate to the max height. That'll get rid of your timer, but you'll still need another boolean to not start randomly falling.
Also, consider Adding platform and wall detection within your jump, as right now you'll magically glide through anything until you reach 5.
Final note: Consider avoding pre-set values for your jumping height. Your jumps will only work if the player is below 5, limiting you to platforms within that range.
I will do you a favor and fix the code, just because I feel nice today. If you wish to try on your own, skip the rest of this post.
if(key_pressed(KEY_SPACE) and me.z==0 and jumpstuntimer.elapsed>=jumpstuntime and jumping==false)
{
jumping=true;
p.play_stationary("sounds/jump.ogg",false);
}
if(jumping==true) //Necessary for the bgt engine to skip over this when a player is just walking. Makes it nicer for BGT overall IMO.
{
if(me.z<5 and risetimer.elapsed>=risetime)
{
risetimer.restart();
me.z+=1;
}
}

if(key_pressed(KEY_SPACE) and me.z==0 and jumpstuntimer.elapsed>=jumpstuntime and jumping==false)
{
jumping=true;
p.play_stationary("sounds/jump.ogg",false);
}
if(jumping==true)
{
if(me.z<5 and risetimer.elapsed>=risetime)
{
risetimer.restart();
me.z+=1;
ascending=true;
}
if(me.z>=5 and ascending==true)
{
ascending=false;
}
if(me.z>1 and ascending==false and risetimer.elapsed>=risetime)
{
risetimer.restart();
me.z-=1;
}
if(me.z==1 and risetimer.elapsed>=risetime)
{
jumping=false;
p.play_stationary("sounds/land.ogg",false);
me.z=0;
}
}

if(me.x<0)
{
me.x=0;
}
else if(me.x>maxx)
{
me.x=maxx;
}
else if(me.y<0)
{
me.y=0;
}
else if(me.y>maxy)
{
me.y=maxy;
}
if(key_pressed(KEY_C))
{
speak(""+me.x+", "+me.y+", "+me.z+"");
}
if(jumping==false)
{
movetime=walkspeed;
}
else if(jumping==true)
{
movetime=airspeed;
}
if(key_down(KEY_UP) and movetimer.elapsed>=movetime)
{
move(1);
}
else if(key_down(KEY_RIGHT) and movetimer.elapsed>=movetime)
{
move(2);
}
else if(key_down(KEY_DOWN) and movetimer.elapsed>=movetime)
{
move(3);
}
else if(key_down(KEY_LEFT) and movetimer.elapsed>=movetime)
{
move(4);
}
if(key_pressed(KEY_ESCAPE))
{
p.destroy_all();
mainmenu();
}
}
wait(5);
}
void move(int dir)
{
movetimer.restart();
if(me.z==0)
{
p.play_stationary("sounds/step"+random(1,5)+".ogg",false);
}
if(dir==1)
{
me.y++;
}
else if(dir==2)
{
me.x++;
}
else if(dir==3)
{
me.y-=1;
}
else if(dir==4)
{
me.x-=1;
}