Sir please clear the error in my fft function sir

   function y = FFT_func(x)
a=size(x);
N=a(2);
n=log2(N);
l=1;
N2=N/2;
NU1=n-1;
k=0;
while(l<=n)
 while(k<=N-1)
 I=1;
 while(I<=N2)
 M=fix(k/(2^NU1));
 b=dec2bin(M,n);
 q=seqreverse(b);
 P=bin2dec(q);
 W=exp(-2*i*P*pi/N);
 T1=W*(x(k+1+N2));
 x(k+1+N2)=x(k+1)-T1;
 x(k+1)=x(k+1)+T1;
 k=k+1;
 I=I+1;
 end
 k=k+N2;
 end