/* ===========================================
   
   filename:  big_integer_addition.c      
   revision:  January 20, 2006

   C Program to read two big integers from a file
   mydata.txt and write the sum to the console.

   Number of digits cannot must be less than
   MAX_DIGITS which is set to be 1,000,000

   Input file has restricted format:

   First integer begins on first line.  If it
   carries over to the next line, this is indicated
   with a backslash character.  The last line of
   the first integer does not have a trailing 
   backslash.

   Exactly one line is skipped between the two integers.
   Then the second integer begins.  Same rules apply
   for formatting the second integer.

   ========================================== */

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

#define MAX_LINE 100
#define MAX_DIGITS 1000000

int main () {

  int i,j,m,n; 
  int empty_line;
  int current_integer = 1;
  int length_one = 0;
  int length_two = 0;
  int length_three = 0;
  int carry;
  int offset;

  char mychar;
  char last_char;
  char p;

  char mystring[150];

  int *bigint1;
  int *bigint2;
  int *bigint3;

  FILE *input_file;

  bigint1 = (int *)malloc((MAX_DIGITS+1)*sizeof(int));
  bigint2 = (int *)malloc((MAX_DIGITS+1)*sizeof(int));
  bigint3 = (int *)malloc((MAX_DIGITS+1)*sizeof(int));

  if (bigint1 == NULL || bigint2 == NULL || bigint3 == NULL) {
    printf("Problem allocating memory for big integers.\n");
    exit(1);
  }

  else {
    printf("Memory for big integers successfully allocated.\n");
  }
  // Open file for reading


  if ((input_file = fopen("mydata.txt","r")) == NULL) {
    printf("Unable to read input file.\n");
    exit(1);
  }
  else {
    printf("Input file successfully opened.\n");
  }

  i = 0;
  current_integer = 1;  
  last_char = '\n';

  while ((mychar=getc(input_file)) != EOF) {
    if(mychar != '\\' && mychar != '\n') {
      if (current_integer == 1) {
        bigint1[i] = mychar-'0';
        length_one++;
        i++;
      }
      if (current_integer == 2) {
        bigint2[i] = mychar-'0'; 
        length_two++;
        i++;
      }
    }
    if (mychar == '\n' && last_char == '\n' && current_integer == 1) {
      current_integer = 2;
      bigint1[i]='\0';
      i = 0;
    }
    last_char = mychar;
  }
  bigint2[i]='\0';
  m = fclose(input_file);
  if (m != 0) { 
    printf("Problem closing input file.\n");
    exit(1);
  }
  else {
    printf("Input file successfully closed.\n");
  }
  printf("Length_one = %d\n", length_one);
  printf("Length_two = %d\n", length_two);
  printf("\n");
  printf("The first integer is:\n");
  i = 0;
  while (length_one - i > 60) {
    for (j = 0; j < 60; j++) {
      printf("%d", bigint1[i]);
      i++;
    }
    printf("\\\n");
  }
  while (i < length_one) {
    printf("%d", bigint1[i]);
    i++;
  }
  printf("\n");
  printf("\n");

  printf("The second integer is:\n");
  i = 0;
  while (length_two - i > 60) {
    for (j = 0; j < 60; j++) {
      printf("%d", bigint2[i]);
      i++;
    }
    printf("\\\n");
  }
  while (i < length_two) {
    printf("%d", bigint2[i]);
    i++;
  }
  printf("\n");
  printf("\n");
  
  for (i = 0, j = length_one - 1; i < j; i++, j--) {
    p = bigint1[i];
    bigint1[i] = bigint1[j];
    bigint1[j] = p;
  }
  for (i = 0, j = length_two - 1; i < j; i++, j--) {
    p = bigint2[i];
    bigint2[i] = bigint2[j];
    bigint2[j] = p;
  }

  i=0;
  carry = 0;
  
  while (i < length_one && i < length_two) {
     bigint3[i] = (bigint1[i] + bigint2[i]+carry)%10;
     carry  = (bigint1[i] + bigint2[i]+carry)/10;
     i++;
  }
  if (length_one == length_two) {
    length_three = length_one;
    if (carry > 0) {
      bigint3[length_one] = carry;
      length_three++;
    } 
  }
  if (length_one > length_two) {
    length_three = length_one;
    while (i < length_one) {
      bigint3[i] = (bigint1[i] + carry)%10;
      carry  = (bigint1[i] + carry)/10;
      i++;
    }
    if (carry > 0) {
      bigint3[length_one] = carry;
      length_three++;
    } 
  }
  if (length_two > length_one) {
    length_three = length_two;
    while (i < length_two) {
      bigint3[i] = (bigint2[i] + carry)%10;
      carry  = (bigint2[i] + carry)/10;
      i++;
    }
    if (carry > 0) {
      bigint3[length_two] = carry;
      length_three++;
    } 
  }
  for (i = 0, j = length_three - 1; i < j; i++, j--) {
    p = bigint3[i];
    bigint3[i] = bigint3[j];
    bigint3[j] = p;
  }
  printf("The sum of these two integers is:\n");
  i = 0;
  while (length_three - i > 60) {
    for (j = 0; j < 60; j++) {
      printf("%d", bigint3[i]);
      i++;
    }
    printf("\\\n");
  }
  while (i < length_three) {
    printf("%d", bigint3[i]);
    i++;
  }
  printf("\n");

  return(0);
}