C++ Program to Multiply Large numbers

C++ program to multiply large numbers has been shown here. This program follows the standard multiplication algorithm.

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1. Program & Output

1. C++ program & output to Multiply Large numbers

Code has been copied

/**************************************
           alphabetacoder.com
 C++ program to multiply large numbers
***************************************/

#include <iostream>
#include <cstring>
 //set maximum size of the input numbers
#define MAX 500

using namespace std;

int main() {
    // declare varables
    char num1[MAX], num2[MAX]; // for storing large numbers.
    int result[2 * MAX] = {0};
    // for storing the result
    int n1, n2, d1, d2, i, j, sum, carry, flag = 0;

    // Read input numbers
    cout << "Enter the first number: ";
    cin >> num1;
    cout << "Enter the second number: ";
    cin >> num2;

    //find the number of digits for both numbers.
    n1 = strlen(num1);
    n2 = strlen(num2);

    // Perform multiplication
    // Multiply each digit of num1 with each digit of num2
    for (i = n1 - 1; i >= 0; i--) {
        // initialize
        carry = 0;
        d1 = num1[i] - '0'; // current digit of first number

        for (j = n2 - 1; j >= 0; j--) {
            d2 = num2[j] - '0'; // current digit of second number
            // calculate sum
            sum = d1 * d2 + result[i + j + 1] + carry;
            result[i + j + 1] = sum % 10;
            // calculate carry
            carry = sum / 10;
        }

        // Set the carry to the leading digit
        result[i] = carry;
    }

    // display the result
    // discard the leading 0s in result array
    cout << "Result = ";
    for (i = 0; i < (n1 + n2); i++) {
        if (result[i])
            flag = 1;
        if (flag)
            cout << result[i];
    }

    return 0;
}

Output

Enter the first number: 12456378945612399785623

Enter the second number: 2315628956456789323

Result = 28844351779058763001834553218068075303229