[ace123]

To search for an object in an array, do a small for loop:

int search_in_table_x(int lookfor)
    int i;
    for (i=0;i<table_length;++i) {
        if (x[i]==lookfor) {
            return i;
        }
    }
    return -1;
}
function Default_Routine(void) {
    int ind, x, y;
    // ...
    ind=search_in_table_x(135);
    if (ind!=-1) {
        x=x[ind];
        y=y[ind];
        pwm03=x; // then do something using those numbers?
        pwm04=y;
    }
}

(Check for -1 after using the function.)

I'm not sure exactly why you need a lookup table.

I'm pretty sure that whatever you are trying to do could be approximated faster and better with a small divide by 16 or something.

One thing to remember is that you shouldn't overcomplicate things like this. Something that can be solved with some complex math function with sines and powers or a lookup table could often be solved just as easily with a simple divide by 8 or scaling and adding without a noticable loss in accuracy.

Imagine if you are at the competition and your robot goes crazy. You would not want to debug through loads of complex math functions. It wouldn't be possible except for an extremely obvious error.
You would end up either wasting all of your precious practice day debugging it and getting nowhere or else giving up and making it simple.