Question

So I have a polynomial that looks like this: -4x^0 + x^1 + 4x^3 – 3x^4
I can tokenize this by space and ‘+’ into: -4x^0, x^1, 4x^3, -, 3x^4

How could I just get the coefficients with the negative sign: -4, 1, 0, 4, -3
x is the only variable that will appear and this will alway appear in order
im planning on storing the coefficients in an array with the array index being the exponent
so: -4 would be at index 0, 1 would be at index 1, 0 at index 2, 4 at index 3, -3 at index 4

Answer 1

Once you have tokenized to “-4x^0”, “x^1”, etc. you can use strtol() to convert the textual representation into a number. strtol will automatically stop at the first non-digit character so the ‘x’ will stop it; strtol will give you a pointer to the character that stoped it, so if you want to be paranoid, you can verify the character is an x.

You will need to treat implicit 1’s (i.e. in “x^1” specially). I would do something like this:

long coeff;
if (*token == 'x')
{
   coeff = 1;
}
else
{
    char *endptr;
    coeff = strtol(token, &endptr, 10);
    if (*endptr != 'x')
    {
        // bad token
    }  
}