跪求大整数(包括负数)四则运算的源代码

大整数肯定是要用字符串存储的，代码如下：

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

#define MAX_SIZE (1024)

char answer[MAX_SIZE];
char answersign;

void bigadd(char * n1, char * n2);
void bigsub(char * n1, char * n2);
void bigmul(char * n1, char * n2);
void bigtrim(char * num, int length);
void bigsort(char * n1, char * n2, int maxlen);
void printnum(char * num);

int main(int argc, char *argv[])
{
int count, index, place;
int len, len1, len2, maxlen;
int i;
char input[MAX_SIZE * 2], num[2][MAX_SIZE];
void (* func)(char *, char *);

scanf("%d", &count);

while (count--) {
scanf("%s", &input);
len = strlen(input);
index = 0;
place = 0;
for (i = len - 1; i >= 0; i--) {
if (input[i] == '+' ||