NCTU LAB 07/05 NUM 2

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

#define MAX 20

void reverseCopy(char *from, char *to){
    int length = strlen(from);
    for(int i=0;i<length;i++){
        to[i] = from[length-i-1];
    }
    to[length]='\0';
}

void mult(char *first, char *sec, char *result){
    char F[MAX],S[MAX],temp[MAX];
    int i, j, r, t_len, carry, res;
    int f_len = strlen(first);
    int s_len = strlen(sec);
    reverseCopy(first,F);
    reverseCopy(sec,S);
    t_len = f_len+s_len;
    r = -1;
    for(i=0;i<=t_len;i++){
        temp[i] = '0';
    }
    temp[i]='\0';
    for(j=0;j<s_len;j++){
            carry = 0;
            for(i=0;i<f_len;i++){
                res = (F[i]-'0') * (S[j] - '0') + carry + (temp[i+j] - '0');
                temp[i+j] = res%10 + '0';
                carry = res/10;
                if(i+j > r){
                    r = i + j;
                }
            }
            while(carry!=0){
                res = carry + temp[i+j] - '0';
                carry = res/10;
                temp[i+j] = res%10 + '0';
                if(i+j > r){
                    r = i + j;
                }
                i++;
            }
        }
        for(;r>0 && temp[r]=='0';r--);
        temp[r+1]='\0';
        reverseCopy(temp,result);
}

int main(){
    char first[MAX], second[MAX], res[MAX];
    while(scanf("%s%s", &first, &second)){
        mult(first, second, res);
        int len = strlen(res);
        printf("Result : ");
        for(int i=0;i<len;i++){
            printf("%c", res[i]);
        }
        printf("\n");
}
return 0;
}