/******************************************
* Section : 15
* Machine No. : N
* Roll No. : 19CS100XY
* Name : Aritra Hazra
* Assignment No : 3B
* Description : School-book Multiplication
******************************************/

#include <stdio.h>

int main( )
{
    unsigned long long int multiplicand, multiplier, i, j, k, l, intrimResult, digitResult, carryResult, stepResult, finalResult, m1, m2, unit1, unit2;

    /* taking two integer inputs */
    printf("Enter Multiplicand: ");
    scanf("%llu", &multiplicand);
    printf("Enter Multiplier: ");
    scanf("%llu", &multiplier);
    
    printf("\n++ School-book Multiplication Procedure ++\n");
    printf("%32llu\n", multiplicand);
    printf("%32llu\n", multiplier);
    printf("---------------------------------\n");
    m2 = multiplier; finalResult = 0; l = 1;
    /* looping for each digit of multiplier */
    while (m2 > 0) {
        m1 = multiplicand;
        unit2 = m2 % 10; /* present LSB of multiplier */
        intrimResult = 0; carryResult = 0; stepResult = 0; k = 1;
        /* looping for each digit of multiplicand */
        while (m1 > 0) {
            unit1 = m1 % 10; /* present LSB of multiplicand */
            
            /* intermediate result generation: digit and carry brakeup */
            intrimResult = (unit1 * unit2 + carryResult);
            digitResult = intrimResult % 10;
            carryResult = intrimResult / 10;
            
            stepResult = stepResult + k * digitResult; /* result obtained each step */
            k = 10 * k;
            m1 = m1 / 10;
        }
        stepResult = stepResult + k * carryResult; /* adjusting the final carry in each step */
        printf("%32llu\n", stepResult * l);
        m2 = m2 / 10;
        finalResult = finalResult + l * stepResult; /* final summed up step results */
        l = 10 * l;
    }
    printf("---------------------------------\n");
    printf("%32llu\n", finalResult);

    return 0;
}