/* mean.c
  
   calculating the mean value of the data in a specified input file.

author:		Leiming Qian <lqian@uiuc.edu> */

#include <stdio.h>

int main(int argc, char *argv[])
{
  /* declaring variables */
  FILE *data_file;
  float mean, data;
  int i;

  /* parsing the command line */
  if (argc!=2) {
    fprintf(stderr, "Usage: mean data_file\n");
    exit(1);
  }
  else {
    if ( !(data_file=fopen(argv[1], "r")) ) {
      fprintf(stderr, "Can't open input file %s\n", argv[1]);
      exit(2);
    }
  }

  /* calculating */
  i=0;
  mean = 0;
  while ( fscanf(data_file, "%f", &data) != EOF ) {
    i++;
    mean += data;
  }
  fclose(data_file);

  mean = mean / (float)i;

  printf("The mean value of data in this file is %f\n", mean);

}