Một cách nhân độc đáo (Phần 2)

Đây là đoạn code do Nhung viết lên, mọi người xem thử nhé.

#include<iostream.h> 
#include<stdio.h> 
#include<stdlib.h> 
#include<string.h> 
#define max 100 
/****/ 
void xuatfile(char *fn); 
void docfile(char *fn,int *&a,int *&b,int &n,int &m); 
void nhan(char *fn,int *&a,int *&b,int **&mt,int n,int m); 
void ghifile(char *fn,int *&a,int n); 
/****/ 
void main() 
{ 
   char *fn="bignum_in.txt"; 
   char *fm="bignum_out.txt"; 

   int *a=new int[max],*b=new int[max];// ab co toi da 100 chu so 
   int n=0,m=0;//la so chu so cua a,b doc tu file,khoi tao =0 
   docfile(fn,a,b,n,m); 
   //tao ma ram luu ket qua nhan tung chu so cua voi b 
   int **mt; 
   mt=new int *[n]; 
   for(int i=0;i<n;i++) 
      mt[i]=new int [m]; 
   nhan(fm,a,b,mt,n,m); 
   //thu hoi mang dong 
   delete a; 
   delete b; 
   for(i=0;i<m;i++) 
      delete []mt[i]; 
   delete[]mt; 
   //xuat ket qua 
   xuatfile(fm); 
} 
/****/ 
void xuatfile(char *fn) 
{ 
   FILE *f; 
   char x; 
   f=fopen(fn,"r"); 
   while(fscanf(f,"%c",&x)&&!feof(f)) 
      cout<<x; 
   fclose(f); 
} 
void docfile(char *fn,int *&a,int *&b,int &n,int &m) 
{ 
   FILE *f; 
   f=fopen(fn,"r"); 
   char x; 
   int i=0,j=0; 
   while(fscanf(f,"%c",&x)&&!feof(f)) 
   { 
      if(x=='n') 
         while(fscanf(f,"%c",&x)&&!feof(f)) 
            b[j++]=x-'0'; 
      else 
         a[i++]=x-'0'; 
   } 
   n=i; 
   m=j; 
   fclose(f); 
} 
void ghifile(char *fn,int *&a,int n) 
{ 
   FILE *f; 
   f=fopen(fn,"w"); 
   char ch; 
   int i=n-1; 
   while(i>0&&a[i]==0) 
      i--; 
   for(;i>=0;i--) 
   { 
    
      ch=a[i]+'0'; 
      fprintf(f,"%c",ch); 
   } 
   fclose(f); 
} 
void nhan(char *fn,int *&a,int *&b,int **&mt,int n,int m) 
{ 
   //mang kq luu ket qua tam thoi 
   int *kq=new int[n*m]; 
   int k=0,i,j; 
   for(i=0;i<n;i++) 
      for(j=0;j<m;j++) 
         mt[i][j]=a[i]*b[j]; 
   //xu ly ma tran 
   kq[k++]=mt[n-1][m-1]; 
   i=n-1; 
   for(j=m-2;j>=0;j--) 
   { 
      int a=i,b=j; 
      kq[k]=0; 
      while(a>=0&&b<m) 
      { 
         kq[k]=kq[k]+mt[a][b]; 
         a--; 
         b++; 
      } 
      k++; 
   } 
   if(j<0) 
      i--; 
   for(;i>0;i--) 
   { 
      int a; 
      kq[k]=0; 
      if(j=m-1&&i<=0) 
         m=m-1; 
      for(a=i,j=0;a>=0&&j<m;a--,j++) 
         kq[k]=kq[k]+mt[a][j]; 
      k++; 
       
   } 
   kq[k]=mt[0][0]; 
   k++; 
   //xu ly mang 
   int nho=0; 
   for(i=0;i<k;i++) 
   { 
      int t; 
      t=kq[i]+nho; 
      nho=t/10; 
      kq[i]=t%10; 
   } 
   if(nho!=0) 
      kq[k++]=nho; 
   //ghi ket qua vao file 
   ghifile(fn,kq,k); 
}