c - Writing data to .cof file -

i'm new coding , have been utterly baffled (for second time today) google can't fix. writing code using code composer 4 on windows. code has no errors fopen("coffic.cof", "w") doesn't change data within file @ (and doesn't create file if file deleted) , can't see why. ideas?

#include "dsk6713_aic23.h"      //codec-dsk support file uint32 fs=dsk6713_aic23_freq_8khz;  //set sampling rate # include <stdio.h> # include <math.h> # include <stdlib.h>  #define pi 3.1415927 #include "coffic.cof"  void main() {     double hpf, fs, fco, atn, fat, tp, k, ad, m, n, o, da, db, dc;     file *fp;     int c, d, e, f, g, h, i, q, r, s, t, u, v;     hpf = 0;            //for high-pass filter input 1, low-pass filter input 0     fs = 8000;          //input samping frequency here     fco = 2400;         //input cut-off frequency here     atn = 17;           //input attenuation (db) here     fat = 3500;         //input frequency of attenuation here     tp = 1/fs;     k = tan(pi*fco*tp);     ad = tan(pi*fat*tp);     m = (log10((pow(10,(atn/10)))-1))/(2*(log10(ad/k)));     o = abs(m);     n = ceil(o);      da = 1.414;     c = (pow(2,15)*k*k/(1+da*k+k*k));     d = (pow(2,15)*2*k*k/(1+da*k+k*k));     e = (pow(2,15)*k*k/(1+da*k+k*k));     q = (pow(2,15)*(2-2*k*k)/(1+da*k+k*k));     r = (pow(2,15)*(-1+k-k*k)/(1+da*k+k*k));      fp = fopen("u:\dsk6713\ivo\csp\coffic.cof", "w");     if (fp == null)     {         printf("error. unable open coffic.cof");         exit(0);     }      fprintf(fp, "int a[3]={%d, d%, %d};\n", c, d, e);     fprintf(fp, "int b[3]={1, d%, %d};\n", q ,r);     fprintf(fp, "int x[3]={0,0,0};\nint y[3]={0,0,0};\n");      fflush(fp);      fclose(fp);      comm_intr();                   //init dsk, codec, mcbsp     while(1);                      //infinite loop }  interrupt void c_int11()         //interrupt service routine  {     short input;     file *fp;     fp = fopen("u:\dsk6713\ivo\csp\coffic.cof", "r");     if (fp == null)     {         printf("error. unable open coffic.cof");         exit(0);     }      fclose(fp);      x[2]=x[1];     x[1]=x[0];     y[2]=y[1];     y[1]=y[0];      input=input_sample();     x[0]=input;      y[0]=a[0]*x[0]+a[1]*x[1]+a[2]*x[2]+b[1]*y[1]+b[2]*x[2];           y[0]=y[0]>>15;                           input=(short)y[0];     output_sample(input);   //output data       return; } 

fp = fopen("u:\dsk6713\ivo\csp\coffic.cof", "w"); 

does not create file assumes have file called coffic.cof on computer. have trouble using write function of fopen use append function. try this

fp = fopen("u:\dsk6713\ivo\csp\coffic.cof", "a"); 

i new programming has worked me when "w" has not.