高精度乘法(高精乘以低精)

#include<bits/stdc++.h>

using namespace std;

const int N = 1e5+5;

char a[N];

struct bign{
    int d[N];
    int len;
    bign(){
        memset(d,0,sizeof(d));
        len = 0;
    }
};

bign change(char *a){
    bign c;
    int len = strlen(a);
    c.len = len;
    for(int i=0; i<len; i++){
        c.d[i] = a[len - i - 1] - '0';
    }
    return c;
}

bign multi(bign a,int k){
    bign c;
    int carry = 0;
    for(int i=0; i<a.len; i++){
        int temp = a.d[i] * k + carry;
        c.d[c.len++] = temp % 10;
        carry = temp / 10;
    }
    while(carry != 0){
        c.d[c.len++] = carry % 10;
        carry /= 10;
    }
    return c;
}

void print(bign c){
    for(int i=c.len - 1; i>=0; i--){
        printf("%d",c.d[i]);
    }
}

int main(){
    int k;
    scanf("%s%d",a,&k);
    bign v = change(a);
    print(multi(v,k));
    return 0;
}