Long Integer Operations

Long Int Addition or Subtraction

#include<iostream>
using namespace std;

int main() {

     int a[] = {9, 8, 5, 2, 8};
     int i = sizeof(a)/sizeof(int);

     int b[] = {0, 1, 7, 4};
     int j = sizeof(b)/sizeof(int);

     int c[((i>j)? (i+1): (j+1))], k = ((i>j)? i: j);

     int carry = 0, remainder, quotient;

     for (i -= 1, j -= 1; i >= 0 && j >= 0; i--, j--) {
          remainder = (a[i] + b[j] + carry) % 10;
          quotient = (a[i] + b[j] + carry) / 10;

          c[k--] = remainder;
          carry = quotient;
     }

     if(j >= 0) {
          for (; j >= 0 ; j--) {
               c[k--] = (b[j] + carry) % 10;   
               carry = (b[j] + carry) / 10;   
          }
     }
     else if(i >= 0) {
          for (; i >= 0 ; i--) {
               c[k--] = (a[i] + carry) % 10;   
               carry = (a[i] + carry) / 10;   
          }
     }
     
     c[0] = carry;

     int size = sizeof(c)/sizeof(int);

     for (i = 0; i < size; i++) {
          cout << c[i] << ' ';
     }

     return 0;
}

Long Int Multiplication

#include<iostream>
using namespace std;

int main() {
     int a[] = {7, 2, 9, 5, 6};
     int b[] = {7, 5, 1, 3};

     int i = sizeof(a)/sizeof(a[0]);
     int j = sizeof(b)/sizeof(b[0]);
     
     const int rows = j;
     const int col = (j * 2) + 1;

     int p = j*2,
     k = 0,
     sum ;

     int twoD[rows][col] = {0};
     for (int i = 0; i < rows; i++) {
          for (int j = 0; j < col; j++) {
               twoD[i][j] = 0 ;
          }
     }
     
     for ( j -= 1; j >= 0; j--) {
          int carry = 0, q = 0;
          for (int r = i-1; r >= 0; r--) {
               sum = ((b[j] * a[r]) + carry);
               twoD[k][p-q] = sum % 10;
               carry = sum / 10;
               q++;
          }
          twoD[k][p-q] = carry;
          k++;
          p--;
     }
     
     for (int i = 0; i < rows; i++) {
          for (int j = 0; j < col; j++) {
               cout << twoD[i][j] << " ";
          }cout << endl;
     }
     
     int carry = 0;
     int res[col]; k = col-1;
     
     for (int i = col-1; i >= 0; i--) {
          sum = 0;
          for (int j = rows-1; j >= 0; j--) {
               sum += twoD[j][i]; 
          } 
          sum += carry;
          res[k] = sum % 10;
          carry = sum / 10;
          k--;
     }
     res[0] = sum;
     cout << "-----------------"<< endl;
     for (int i = 0; i < col; i++) {
          cout << res[i] << " ";
     }
}