Ultraviolet A 10106 product (multiply by a large number)

Product

The Problem

The problem is to multiply two integers x, y .(0 <= X, Y <10250)

The input

The input will consist of a set of pairs of lines. Each line in pair contains one multiplyer.

The output

For each input pair of lines the output line shoshould consist one integer the product.

Sample Input

12122222222222222222222222222

Sample output

144444444444444444444444444

Multiply large numbers. There are many templates on the Internet. I wrote them myself this afternoon and ignored the front 0, resulting in 0*12 = 123, 0 * = 000, then the output is changed to AC.

#include <iostream>#include <cstring>#define maxn 260using namespace std;int main(){    char str1[maxn],str2[maxn];    while(cin>>str1>>str2){int len1,len2;len1=strlen(str1);len2=strlen(str2);int s1[maxn],s2[maxn];memset(s1,0,sizeof(s1));memset(s2,0,sizeof(s2));int i;for(i=0;i<len1;i++)s1[i]=str1[i]-'0';for(i=0;i<len2;i++)s2[i]=str2[i]-'0';int sum[maxn+maxn];memset(sum,0,sizeof(sum));int j,k;for(i=len2-1;i>=0;i--){for(j=len1-1;j>=0;j--){sum[i+j+1]=sum[i+j+1]+s2[i]*s1[j];}}for(k=len1+len2-1;k>=0;k--)if(sum[k]>=10){int temp;temp=sum[k]%10;sum[k-1]=sum[k-1]+sum[k]/10;sum[k]=temp;}//if(sum[0]!=0)//cout<<sum[0];bool flag=0;for(i=0;i<len1+len2-1;i++){if(sum[i]!=0)flag=1;if(flag==1)cout<<sum[i];}cout<<sum[len1+len2-1];cout<<endl;}    return 0;}