Bounce a character around the screen using for loops & gotoxy

[K.A.J]

Greets all,

I'm following some examples of using the gotoxy function from a c book that i am reading, and can't seem to get the quiz/task. Here's how it goes, i am trying to get the character O to bounce around the screen, using a few four loops and the goto function. I am able to get the character to go diagonally accross the screen with...

 void main(void)
{ int x,y,z;

for(x=0,y=0,z=0;z<5000;x++,y++,z++)
	{
	  gotoxy(x,y);
	  printf("O");
	  delay(100);
	  clrscr();
 	}
getch();
}

But i want the character 'ball' to bounce around the screen. I asked my programming teacher to give me tips, but i asked him not to give me the answe completely else i won't learn anything. He said that i needed, 4 if statements, which i have tried adding into the code, but to no avail. I have now given up, and would like to find out the answer as i'm ripping my hair out.

[Stef]

Basically, those four if statements would detect if the ball touches the edges of the screen (one if-statement for each edge), and reverse its speed if it does.
Oh, this assumes a screen from 0-80 horizontally, and 0-25 vertically, adjust the values as needed

void main(void)
{ 
  int x,y,z;
  int vx = 1;
  int vy = 1;

  for(x=0,y=0,z=0;z<5000;x+=vx,y+=vy,z++)
  {
    if( x<0 )
    {
      vx = 1;
      x = 0;
    }
    if( x>80 )
    {
      vx = -1;
      x = 80
    }
    if( y<0 )
    {
      vy = 1;
      y = 0;
    }
    if( y > 25 )
    {
      vy = -1;
      y = 25;
    }
    gotoxy(x,y);
    printf("O");
    delay(100);
    clrscr();
  }
  getch();
}

[K.A.J]

Thankyou, It all seems so straight forward after you see what you were doing wrong.