C++ 大数乘法 一般算法

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

#define MAX 10001 

int bigchenfa(int *sum,int *a,int *b,int lsum,int la,int lb) 
{ 
    int i,j,k ; 
    memset(sum,0,sizeof(sum)); 
    lsum = 0 ; 
    for(i=1 ; i<= la ; i++) /*用数组模拟运算*/ 
    for(j=1,lsum=i-1; j<= lb ; j++) 
    sum[++lsum] += b[j] * a[i] ; 
     
    for(i=1 ; i<= lsum ; i++)/*进位处理*/ 
    if (sum[i] >= 10) 
    { 
               if ( sum[lsum] >= 10) 
               lsum ++ ; 
               sum[i+1] += sum[i] / 10 ; 
               sum[i] %= 10 ; 
    } 
     
    return lsum ; 
} 

     
int main(void)