#include <stdio.h>
#include <stdlib.h>

int main() {
  int k;
  FILE *fp;
  fp = fopen("/tmp/file.txt", "wt");
  if (fp == 0) {
    perror("fopen");
    exit(1);
  }
  k = 3;
  fprintf(fp, "Prima riga\n");
  fprintf(fp, "Seconda riga con un numero: %d\n", k);
  fclose(fp);
}