trying to read mopac parameters from the input file in C

internal.c

#include <stdio.h>
#include <string.h>
#include <ctype.h>

/*
  INTERNAL keyword requested by INTERNAL=block_name, where the parameters are
  included in the same format used by EXTERNAL but inside of a block started by
  block_name and ended "end block_name"
 */

/*
  read parameters from `fname` into `params`
 */
int read_internal(char* fname, char* params) {
  FILE *input = fopen(fname, "r");
  if (input == NULL) {
    return 1;
  }
  char line[100];
  int in_params = 0;
  char block_start[100];
  char block_end[100] = "end ";
  char *param_ptr = params;
  while (fgets(line, 100, input) != NULL) {
    /* determine block_name by taking apart keywords */
    if (strstr(line, "internal=") != NULL) {
      char *l = strtok(line, "=");
      while (strstr(l, "internal") == NULL) {
	l = strtok(NULL, "=");
      }
      /* l here contains the block_name but may be followed by whitespace and/or
	 the start of another keyword, so save only the part we want */
      l = strtok(NULL, "=");
      int i = 0;
      while(!isspace(*l)) {
	  block_start[i] = *l;
	  block_end[4 + i++] = *l++;
	}
    } else if (strstr(line, block_end) != NULL) {
      in_params = 0;
    } else if (strstr(line, block_start) != NULL) {
      in_params = 1;
    } else if (in_params) {
      char* p = line;
      while(*p != '\0') {
	*param_ptr++ = *p;
	p++;
      }
    }
  }
  return 0;
}

int main(int argc, char *argv[]) {
  char params[1000];
  int c = read_internal(argv[1], params);
  printf("%s\n", params);
  return 0;
}