unknown parse error when testing function - c

Question

I have the function below which seems to act as it should, however when running the program through a testing program, I am given the errors: parse error: [int xSwapped = ((255 << nShift) | (255 << mShift));] and
undeclared variable `xSwapped': [return (~xSwapped & x) | nMask | mMask;]
int dl15(int x, int n, int m){
// calculates shifts, create mask to shift, combine result
// get number of bytes needed to shift, multiplying by 8
// get Masks by shifting 0xff and shift amount
// shift bits to required position
// combine results
int nShift = n<< 3;
int mShift = m<< 3;
int nMask = x & (255 << nShift);
int mMask = x & (255 << mShift);
nMask = 255 & (nMask >> nShift);
mMask = 255 & (mMask >> mShift);
nMask = nMask << mShift;
mMask = mMask << nShift;
int xSwapped = ((255 << nShift) | (255 << mShift));
return (~xSwapped & x) | nMask | mMask;
}
Not certain what im missing, thank you.

Answer 1

It looks like you are using a C compiler set to an old C standard. Prior to C99 you could not put executable statements before declarations.
You can fix this by moving the declaration of xSwapped to the top:
int nShift = n<< 3;
int mShift = m<< 3;
int nMask = x & (255 << nShift);
int mMask = x & (255 << mShift);
int xSwapped; // Declaration
nMask = 255 & (nMask >> nShift);
mMask = 255 & (mMask >> mShift);
nMask = nMask << mShift;
mMask = mMask << nShift;
xSwapped = ((255 << nShift) | (255 << mShift)); // Assignment
return (~xSwapped & x) | nMask | mMask;