程序代码：

#include<stdio.h>
#include<string.h>
#define N 101

void Init(char a[]);
char* fun(char a[],char b[],char c[]);

int main()
{
    char a[N+1]={0};                                //默认A比B长
    char b[N+1]={0};
    char c[N+2]={0};

    Init(a);
    Init(b);

    printf("%s\n",fun(a,b,c));

    return 0;
}

void Init(char a[])
{
    char c=0;
    int i=1;

    a[0]='0';

    while ((c=getchar())!='\n')
        a[i++]=c;
}

char* fun(char a[],char b[],char c[])
{
    char* pa=a+strlen(a)-1;                                      //*pc+=((*pa-'0')+(*pb-'0'))
    char* pb=b+strlen(b)-1;
    char* pc=c+N-2;
    int s=0;

     while(pb!=b)
     { 
         char* pa=a+strlen(a)-1;
         int jin=0;
           while(pa!=a)
           { 
               if((*pa-'0')*(*pb-'0')>=10)
               {
                   *pc=*pc+((*pa-'0')*(*pb-'0')+jin)%10;                     //进位与入数组
                    jin=((*pa-'0')*(*pb-'0'))/10;
               }              
               else if(((*pa-'0')*(*pb-'0'))<10)                                          
               {   
                   *pc=*pc+((*pa-'0')*(*pb-'0'))+jin;  
               }
               if((*pc-'0')>=10)
               {  
                   *(pc-1)+=1;
                   *pc=(*pc-'0')%10;         
               }
               --pa;
               --pc;                        
           }
           s++;
           --pb;
           pc=c+N-2-s;     
     }
    return (pc+s+strlen(c)-1);
}