两位数的大数乘法

# include <iostream>
# include <cstdio>
# include <cstring>
# include <algorithm>

using namespace std;

int main(){

    int a[30],b[30];
    int result[30];
    char st1[30],st2[30];

    scanf("%s%s",st1,st2);
    int len1,len2;
    len1 = strlen(st1);
    len2 = strlen(st2);

    for(int i=0;i<len1;i++)
        a[len1-i-1] = st1[i] - '0';
     for(int i=0;i<len2;i++)
        b[len2-i-1] = st2[i] - '0';

 memset(result,0,sizeof(result));
    for(int i=0;i<len1;i++){
        for(int j=0;j<len2;j++){
            result[i+j] += a[i]*b[j];

        }
    }



    for(int i=0;i<len1+len2-1;i++){
        result[i+1]+= result[i]/10;
        result[i] = result[i]%10;
    }


    if((len1==1&&a[0]==0)||(len2==1&&b[0]==0))
        printf("%dn",result[0]);
    else
    for(int i=len1+len2-1;i>=0;i--){
        if(i==(len1+len2-1)&&result[i]==0)  continue;
        printf("%d",result[i]);
    }
    printf("n");


    return 0;
}