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

void read_numbers(FILE* fp1, FILE* fp2, FILE* fp3);

void swap(int* a, int* b);

int main(void)
{
    // read all file at once
   FILE *fp1 = fopen("numbers1.txt", "r");
   FILE *fp2 = fopen("numbers2.txt", "r");

   // Open file to store the result
   FILE *fp3 = fopen("output.txt", "w");
   //char c;

   if (fp1 == NULL || fp2 == NULL || fp3 == NULL)
   {
         printf("Could not open files");
         exit(1);
   }

   //function to read file 1 and 2, compare it, and output to fp3.
   read_numbers(fp1,fp2,fp3);

   fclose(fp1); fp1 = NULL;
   fclose(fp2); fp2 = NULL;
   fclose(fp3); fp3 = NULL;

    return 0;
}

void read_numbers(FILE* fp1, FILE* fp2, FILE* fp3)
{
    int number1, number2;
    int noc1;
    int noc2;
    int smaller;

    noc1 = fscanf(fp1, "%d", &number1);
    noc2 = fscanf(fp2, "%d", &number2);
    while (noc1 == 1 && noc2 == 1)
    {
        if(number1 <= number2)
        {
          smaller = number1;
          noc1 = fscanf(fp1, "%d", &number1);
        }
        else
        {
          smaller = number2;
          noc2 = fscanf(fp2, "%d", &number2);
        }
        fprintf(fp3, "%d\n",smaller);
    }
    while(noc1 == 1) // If file 1 has stuff
    {
      fprintf(fp3, "%d\n",number1 );
      noc1 = fscanf(fp1, "%d", &number1); // read it and dump it into fp3
    }

    while (noc2 == 1)
    {
      //printf("HI %d\n", number2);
      fprintf(fp3, "%d\n",number2);
      noc2 = fscanf(fp2, "%d", &number2); // read it and dump it into fp3
    }
}