Public Group

# Why isn't this moving?

This topic is 2031 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

I am trying to create a program that will randomly generate rooms as the user presses the arrow keys, and it's been working fine, but I've hit a bit of a snag.  I'm trying to get the key press commands working, but no matter how long I look at the code, I can't figure out why the little figure I have made isn't moving.

I've included the entire file for the program, but here is where I think the problem is taking place:


while(SDL_PollEvent(&Event))
{
if(Event.type == SDL_KEYDOWN)
{
if (Event.key.keysym.sym)
{
if (SDL_KEYDOWN == SDLK_UP)
{
if (PlayerLocationy == 0)
{
Message = DeniedMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);
Message == NULL;
}
else
{
PlayerLocationy =- 42;
ApplySurface(0,421,Sprites,Screen,&TextBox);
}
}
if (SDL_KEYDOWN == SDLK_DOWN)
{
if (PlayerLocationy == 378)
{
Message = DeniedMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);
Message == NULL;
}
else
{
PlayerLocationy =+ 42;
ApplySurface(0,421,Sprites,Screen,&TextBox);
}
}
if (SDL_KEYDOWN == SDLK_LEFT)
{
if (PlayerLocationx == 0)
{
Message = DeniedMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);
Message == NULL;
}
else
{
PlayerLocationx =- 42;
ApplySurface(0,421,Sprites,Screen,&TextBox);
}
}
if (SDL_KEYDOWN == SDLK_RIGHT)
{
if (PlayerLocationy == 0)
{
Message = DeniedMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);
Message == NULL;
}
else
{
PlayerLocationy =+ 42;
ApplySurface(0,421,Sprites,Screen,&TextBox);
}
}
if (SDL_KEYDOWN == SDLK_UP)
{
Message == EscapeMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);

if (SDL_KEYDOWN == SDLK_y)
{
QUIT == true;
}
}
}
}

if(Event.type == SDL_QUIT)
{
QUIT = true;
}
}


Any help that could be given would be very much appreciated.  I have a feeling it's something smal like a missing = sign that I can't find, but maybe another programmer would be able to see what I have not.

-Programmer557

[attachment=15821:Randomized Maze Game.zip]

##### Share on other sites

if (Event.key.keysym.sym)
{
if (SDL_KEYDOWN == SDLK_UP)
{

I'm not familiar with SDL, but that just looks wrong. Shouldn't it be more along those lines?

if (Event.key.keysym.sym == SDLK_UP)
{

Right now you are appearantly comparing the event-constant with the key-constant in the latter if, and as for the first one, I don't think that is necessary - is "Event.key.keysym.sym" a pointer? You are basically checking if this variable is any other value than 0, can't tell if this is what you intended or not.

Edited by Juliean

##### Share on other sites

if (Event.key.keysym.sym)
{
if (SDL_KEYDOWN == SDLK_UP)
{

I'm not familiar with SDL, but that just looks wrong. Shouldn't it be more along those lines?

>if (Event.key.keysym.sym == SDLK_UP)
{

Right now you are appearantly comparing the event-constant with the key-constant in the latter if, and as for the first one, I don't think that is necessary - is "Event.key.keysym.sym" a pointer? You are basically checking if this variable is any other value than 0, can't tell if this is what you intended or not.

Yes, you're correct. SDL_KEYDOWN is a constant used to determine the type of the event.

Event.key.keysym.sym is an integer containing the key symbol representing which key was pressed.

##### Share on other sites

if (PlayerLocationy == 378)
{
Message = DeniedMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);
Message == NULL;
}

if (SDL_KEYDOWN == SDLK_y)
{
QUIT == true;
}

I am almost 100% positive you mean to use a single equals sign here. Double equals compares them for equality, and then the result is discarded here with nothing happening.

else
{
PlayerLocationy =+ 42;
ApplySurface(0,421,Sprites,Screen,&TextBox);
}

else
{
PlayerLocationx =- 42;
ApplySurface(0,421,Sprites,Screen,&TextBox);
}

I can't quite place what language you must be getting this from, but in compound assignment operators, the equals sign always comes last. "PlayerLocationy =+ 42;" is parsed the same as "PlayerLocationy = +42;", which isn't what you wanted. Likewise, "PlayerLocationy =- 42;" is the same as "PlayerLocationy = -42;".

##### Share on other sites

Also, you should use

int x;

if( x == 0)
{
}
else if(x == 1)
{
}


for mutually exclusive conditions. Or better yet:

int x;

switch(x)
{
case 0:
// ...
break;
case 1:
// ...
break;
}


as long as you have an enumarable variable (which you should have with the SDL-event, just change "x" with Event.type and use "SDL_KEYDOWN" etc... in the "case" statement). Both of these will not only help performance, but also make your code more understandable.

##### Share on other sites

I found a little bit later that I had forgotten to flip the screen, but even after adding that the program still doesen't do what I want it to.  Just thought I'd add that before anyone made the comment.

##### Share on other sites

I think you're going to save yourself a lot of time, now and in the future, if you immediately remove all the repetition here. As it is, any change you make to the core routine here has to be made 4 times, and that means 4 times the probability that you'll make another mistake.

DRY

.

Edited by Six222

##### Share on other sites

.

That's exactly what I was saying. It was clear that he wanted to add to and subtract from the variables, but the order of the two symbols in compound operators is standardized. The equals sign must come last, otherwise, whenever he moves, it will only allow him to move to -42 or 42 on either axis, which I can guarantee is not what he wanted to do for a room generator, unless he only wants 7 rooms maximum, some he can only visit once.

I'll accept the downvote, anyway.

##### Share on other sites

if (SDL_KEYDOWN == SDLK_UP)
{
Message == EscapeMessage;
ApplySurface((ScreenWidth - Message->w)/2,(ScreenHeight - Message->h + 420)/2,Message,Screen,NULL);

if (SDL_KEYDOWN == SDLK_y)
{
QUIT == true;
}

}

I just notice on another read-through, that this condition will never be true. A key press event only contains information on one key press; to get another key press, you have to check for the next event. Even if we were checking which key was pressed correctly here, the nested condition will never be true, because we just checked to see if the same value was equal to SDLK_UP before entering the if-block.

1. 1
2. 2
3. 3
Rutin
15
4. 4
5. 5
khawk
11

• 10
• 9
• 9
• 11
• 11
• ### Forum Statistics

• Total Topics
633679
• Total Posts
3013301
×