Timing delay on my PIC - delay

Question

Prepare for a nooby question.
I'm writing some ultra-simple code for this new PIC which I've just got. All I'm trying to do is to flash an LED. Below are two code samples - the first works but the second doesn't. Why?? I can't see any problem with the second one.
WORKS:
while(1)
{
i=99999;
while(i--) {
LATAbits.LATA0 = 0; // set RA0 to logic 1
}
i=99999;
while(i--) {
LATAbits.LATA0 = 1; // set RA0 to logic 0
}
}
DOESN'T WORK:
while(1)
{
LATAbits.LATA0 = 1; // set RA0 to logic 1
for(i=0;i<99999;i++) {}
LATAbits.LATA0 = 0; // set RA0 to logic 0
for(i=0;i<99999;i++) {}
}
Thanks in advance for the help!

Answer 1

Try this:
while(1)
{
for(i=0;i<99999;i++)
{
LATAbits.LATA0 = 1; // set RA0 to logic 1
}
for(i=0;i<99999;i++)
{
LATAbits.LATA0 = 0; // set RA0 to logic 0
}
}
Maybe your compiler is optimizing and ignoring the for statements as they have no code to execute inside. What I did was put the RA0 assignment inside these statements, forcing the compiler to keep the delay loops.
You can also pass the argument -S to your compiler to see the assembly code generated and confirm that the for statements were removed. The -S option generates an intermediate file with a ".S" extension.

Answer 2

What's your definition of i? char i? int i? long i?
What PIC are you using?
If you're using an int, the 8-bit PICs use a 16-bit int.
So what happens:
// Try to stuff 99999 into 16-bits, but it becomes 34463
i=99999;
// Count-down from 34463 to zero
while(i--) {}
// Successfully exit delay
As opposed to:
// Count up from zero
// Get to 65535 and then reset to zero
// Never reach 99999
for(i=0;i<99999;i++) {}
// Never exit delay
Try using unsigned long int for i, which tends to be 32-bit on PICs and see if it starts to work.