If statements

Note that 5 bits can be converted into a number 0..31.

So:

unsigned char val;
unsigned char prev_val;

prev_val = 255;
for (;;) {
    for (;;) {
        val = 0;
        if (thinking) val |= 1;
        if (easy) val |= 2;
        if (medium) val |= 4;
        if (hard) val |= 8;
        if (val != prevval) {
            switch (val) {
                case 1:
                case 3:
                case 7:
                case 15:
                    yellow_led = (val & 1) ? ON : OFF;
                    green_led = (val & 2) ? ON : OFF;
                    amber_led = (val & 4) ? ON : OFF;
                    red_led = (val & 8) ? ON : OFF;
                    break;
                default:
                    // invalid combination
                    yellow_led = green_led = amber_led = red_led = OFF;
                    // do a continue here if invalid combinations should break loop.
            }
            break; // end this loop, since you had a change
        }
    } // loop until a change found (or maybe a change to another valid value)
    prev_val = val;
    // do something fancy now when you know you have a change (or the first time)
    ...
}

Note that 5 bits can be converted into a number 0..31.

So:

unsigned char val;
unsigned char prev_val;

prev_val = 255;
for (;;) {
    for (;;) {
        val = 0;
        if (thinking) val |= 1;
        if (easy) val |= 2;
        if (medium) val |= 4;
        if (hard) val |= 8;
        if (val != prevval) {
            switch (val) {
                case 1:
                case 3:
                case 7:
                case 15:
                    yellow_led = (val & 1) ? ON : OFF;
                    green_led = (val & 2) ? ON : OFF;
                    amber_led = (val & 4) ? ON : OFF;
                    red_led = (val & 8) ? ON : OFF;
                    break;
                default:
                    // invalid combination
                    yellow_led = green_led = amber_led = red_led = OFF;
                    // do a continue here if invalid combinations should break loop.
            }
            break; // end this loop, since you had a change
        }
    } // loop until a change found (or maybe a change to another valid value)
    prev_val = val;
    // do something fancy now when you know you have a change (or the first time)
    ...
}

Thanks for your time. It has helped me a great deal.

The comment:

// do a continue here if invalid combinations should break loop

should of course be

// do a continue here if invalid combinations shouldn't break the loop

I noticed that. I have it working now. Thanks. Also another question that has been bugging me. I'm using external memory with the 8051. I can only write 1 byte at a time. I'm using a function to write to external memory that puts the byte on the port 1 byte at a time. Problem is that my function will take in more than a byte at times. I don't understand how to write to this external writing function.

I'm using a function to write to external memory that puts the byte on the port 1 byte at a time. I don't understand how to write to this external writing function.
what are you talking about, you are coding in 'C' so why would you have "a function to write to external memory".

Erik

Because he is manually driving the ports to write to external memory instead of having the processor directly access the memory using xdata accesses. Everything is possible, even if most people would prefer the processor to do the work.

that he has never seen ths XDATA keyword?

Everything is possible
try striking a match on a bar of soap :)

Erik

I have to write the function to get the timing right for the type of external memory chip i'm using. So will I need to split up the data into bytes some way?

So will I need to split up the data into bytes some way?
I do not understand what you mean
you can, of course, only read or write to one memory address (one byte for 8-bit wide memory) at a time.

Erik

Why be vague, what type.
But Yes you take your data break it up into bytes. Write one, inc the address and repeat until done.

How to break up the data there are several ways. shifts, pointers, and unions are some.