大数运算 C++

#include <string>  
#include <iostream> 
using namespace std; 
char num[4][100];
char s[100];
int main() 
{ 
	void swi();
	void clear(char *s);
	void add(char *s1,char *s2,char *s);
	while(cin>>num[0]>>num[1]>>num[2]){
		for(int i = 0; i < 97; i++){
			add(num[0],num[1],s);
			add(num[2],s,num[3]);
			strcpy(num[0],num[1]);
			strcpy(num[1],num[2]);
			strcpy(num[2],num[3]); 
		}
			cout << num[3] << endl;
			clear(s);
			clear(num[3]);
	}
	return 0; 
} 
void clear(char *s)
{
	while(*s)
		*s++ = '\0';
}
void add(char *s1,char *s)
{
	void swi(char *s);
	int flag = 0;
	int i = 0;
	char *p1 = s1;
	char *p2 = s2;
	while(*p1 != '\0')
		p1++;
	while(*p2 != '\0')
		p2++;
	--p1,--p2;
	while(p1 != s1-1 && p2 != s2-1){
		s[i] = (flag + *p1-'0'+ *p2-'0')%10 +'0';
		i++;
		if(*p1-'0' + *p2-'0' +flag > 9)
			flag = 1;
		else
			flag = 0;
		p1--,p2--;
	}
	if(p1 == s1-1){
		while(p2 != s2-1){
		s[i] = (flag + *p2 -'0')%10 + '0';
		i++;
		if(*p2-- -'0' + flag > 9)
			flag = 1;
		else 
			flag = 0;
		}
	}
	else 
		while(p1 != s1-1){
		s[i] = (flag + *p1 -'0')%10 + '0';
		i++;
		if(flag + *p1-- -'0' > 9)
			flag = 1;
		else
			flag = 0;
		}
	if(flag) 
		s[i] = '1';
	s[++i] = '\0';
	swi(s);
}
void swi(char *s)
{
	int i ;
	int j = strlen(s)-1;
	char c;
	for(i=0; i < strlen(s)/2; i++,j--){
		c    = s[i];
		s[i] = s[j];
		s[j] = c;
	}
}