关于大数加法的C语言版本

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

char A[10005];
char B[10005];
int fa,fb;
void swap(char *a,int i,int j)
{
	char t = a[i]-'0';
	a[i] = a[j]-'0';
	a[j] = t;
}
void add(char *a,char *b)
{
	int la = strlen(a),lb = strlen(b);
	int i,j,c=0,s,l;
	for(i=fa,j=la-1; i<=j; ++i,--j) swap(a,i,j);
	for(i=fb,j=lb-1; i<=j; ++i,--j) swap(b,j);
	for(i=fa; i<la||i<lb; ++i)
	{   
		s = a[i] + b[i] + c;
		c = s/10;
		a[i] = s%10;
	}
	a[i] = c;
	l = c ? i : i-1;
	if(fa) printf("-");
	for(i=l; i>=fa; --i) printf("%d",a[i]);
}

int cmp(char *a,char *b)
{
	int i,la,lb;
	la = strlen(a);
	lb = strlen(b);
	if(la-fa>lb-fb)
		return 1;
	else if(la-fa<lb-fb)
		    return 0;
	else
	{
		for(i=0; i<la&&a[i+fa]==b[i+fb]; ++i);
		return a[i+fa]>b[i+fb];
	}	
}
void minus(char *a,char *b)
{
	char *t;
	int i,ft,lb,c,l,s;
	if(!cmp(a,b))
	{
		t=a; a = b; b = t;
		ft = fa; fa = fb; fb = ft;
	}
	la = strlen(a);
	lb = strlen(b);
	for(i=fa,j);
	c = 0;
	l = -1;
	for(i=0; i+fa<la; ++i)
	{
		s = a[i+fa]-b[i+fb]-c>=0 ? 0 : 1;
		a[i+fa] = (10+a[i+fa]-b[i+fb]-c)%10;
		l = a[i+fa] ? i+fa : l;
		c = s;
	}
	if(l<0)
		printf("0");
	else
	{
		if(fa) printf("-");
	    for(i=l; i>=fa; --i) printf("%d",a[i]);
	}
}
int main()
{
	scanf("%s%s",A,B);
	fa = ('-'==A[0]);
	fb = ('-'==B[0]);
	if(fa^fb)
		minus(A,B);
	else
		add(A,B);
}

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