fileaddsub.c

/***************************************
 * Read in a file of the following form:
 * the file begins with a number n, and
 * then has n lines, each containing one
 * number.  Your goal is to keep a running
 * sum where the first number is added, the
 * second subtracted, the third added, the
 * fourth subtracted, and so on.  The file's
 * name is input by the user.
 ***************************************/
#include "si204.h"

int main() {
  // Get file name
  cstring fname;
  fputs("Filename: ", stdout);
  readstring(fname, stdin);

  // Open file and read n - we really should check that the file was found!
  stream fin = fopen(fname, "r");

  // read the first number, which is the number of lines
  int numlines = readnum(fin);

  // read and sum values
  int sum = 0;
  for(int i=0; i < numlines; i++) {
    int next = readnum(fin);
    if (i % 2 == 0) {
      sum += next;
    } else {
      sum -= next;
    }
  }

  // close file
  fclose(fin);

  // print result
  writenum(sum, stdout);
  fputs("\n", stdout);

  return 0;
}