Умножение больших чисел

        const int N = 300;
    char number1[N], number2[N];
    int size1, size2;
    cin >> number1 >> number2;
 
    size1 = strlen(number1);
    size2 = strlen(number2);
 
    int size;   //define the largest size in order the rest will be cpmpleted 0
    size1 >= size2 ? size = size1 : size = size2;
 
 
    int *a = new int[size]();   //nullify the arrays
    int *b = new int[size]();       //possible, the size of array can be equal size/6 (with the rounding up)
 
 
                                    //define the sign and fill in the array
    fillMas(a, number1, size1);
    fillMas(b, number2, size2);
 
    //define size new massive (6 digits)
    size % 6 == 0 ? size = size / 6 : size = (size / 6) + 1;
}
void fillMas(int* a, char* number, int size) {
    int i = 0;
 
    if (number[0] == '+' || number[0] == '-')
        i = 1;
 
    for (int j = size - 1, count = 0; j >= i; count++) {
        for (int agent = 0; agent < 6; agent++, j--) {
            if (j < i)
                break;
 
            a[count] += (number[j] - '0')*pow(10, agent);
        }
    }
 
}
   int* mul(int* a, int* b, int size) {
    int *sol = new int[size * 2]();
 
    for (int i = 0; i < size; i++) {
        for (int j = 0; j < size; j++) {
            __int64 k = (__int64)a[i] * (__int64)b[j] + sol[i + j];
            sol[i + j] = k % 1000000;
            sol[i + j + 1] = k / 1000000;
        }
    }
    return sol;
}

const int64_t base = 1e9;