void    save_data()
{
        long k;
		int  k1;
		extern long npt;
		extern complex x[size];

		if((out=fopen("dftout.dat","w"))==NULL)
		{
		       printf("cannot open file dftout.dat\n");
			   exit(1);
		}
		fprintf(out,"k \tXR(k) \t\tXI(k)\n");
        fprintf(out,"\n");
		for(k=1;k<=npt;++k)
		{
		       k1=k-1;
			   fprintf(out,"%d \t%f \t%f \n",k1,x[k].real,x[k].imag);
		}
		fclose(out);
}