大整数的加减乘除

/*大整数运算*/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define MAX 100

char* add(char* a,char* b);
char* sub(char* a,char* b);
char* mul(char* a,char* b);
char* div(char* a,char* b);
bool isValid(char* a,int n);
char* add_core(char* a,char* b);
char* sub_core(char* a,char* b);
char* mul_core(char* a,char* b);
char* div_core(char* a,char* b);
int main()
{
	char* a;
	char* b;
	a=(char*)malloc(sizeof(char)*MAX);
	b=(char*)malloc(sizeof(char)*MAX);
	scanf("%s",a);
	scanf("%s",b);
	if(isValid(a,strlen(a)) && isValid(b,strlen(b)))
	{
		printf("a+b=%s\n",add(a,b));
		//add(a,b);
		printf("a-b=%s\n",sub(a,b));
		printf("a*b=%s\n",mul(a,b));
		printf("a/b=%s\n",div(a,b));
	}
	else
	{
		printf("invalid input\n");
	}
	return 0;
}
bool isValid(char* a,int n)
{
    int i;

	if(a==NULL || n<=0)
		return false;
	if(!(a[0]=='-' || (a[0]>='0' && a[0]<='9')))
		return false;
	if(a[0]=='0' && a[1]!='\0')
		return false;
	for(i=1;i<n;i++)
		if(a[i]<'0' || a[i]>'9')
			return false;
	return true;
}
char* add(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1>len2?len1:len2;
	char* c;
	c=(char*)malloc(sizeof(char)*(len+3));
    if(a[0]!='-' && b[0]!='-')//a+b
	{
		return add_core(a,b);
	}
	else if(a[0]=='-' && b[0]=='-')//-a-b
	{
		c[0]='-';
		c[1]='\0';
		strcat(c,add_core(a+1,b+1));
        return c;
	}
	else if(a[0]=='-' && b[0]!='-')//-a+b
	{
		return sub(b,a+1);
	}
	else if(a[0]!='-' && b[0]=='-')//a-b
	{
		return sub(a,b+1);
	}
}
char* add_core(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1>len2?len1+1:len2+1;
	char* c;
	int i=len-1,carry=0,temp;
	int index1=len1-1,index2=len2-1;
	c=(char*)malloc(sizeof(char)*(len+1));
	c[len]='\0';
    while(index1>=0 && index2>=0)
	{
		temp= a[index1--]-'0' + b[index2--]-'0' + carry;
		if(temp>=10)
		{
			carry=1;
			c[i--]=temp-10+'0';
		}
		else 
		{
		    carry=0;
			c[i--]=temp+'0';
		}
	}
	while(index1>=0)
	{
		temp= a[index1--]-'0'+carry;
		if(temp>=10)
		{
			carry=1;
			c[i--]=temp-10+'0';
		}
		else 
		{
		    carry=0;
			c[i--]=temp+'0';
		}
	}
    while(index2>=0)
	{
		temp= b[index2--]-'0'+carry;
		if(temp>=10)
		{
			carry=1;
			c[i--]=temp-10+'0';
		}
		else 
		{
		    carry=0;
			c[i--]=temp+'0';
		}
	}
	c[i]=carry+'0';
	i=0;
	while(c[i]=='0')
		i++;
    return c+i;
}
char* sub(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1>len2?len1:len2;
	char* c;
	c=(char*)malloc(sizeof(char)*(len+2));
	if(a[0]!='-' && b[0]!='-')//a-b
	{
		if(len1>len2 || (len1==len2 && strcmp(a,b)>0))
			return sub_core(a,b);
		else if(len1<len2 || (len1==len2 && strcmp(a,b)<0))
		{
			c[0]='-';
			c[1]='\0';
			strcat(c,sub_core(b,a));
			return c;
		}
		else if(strcmp(a,b)==0)
		{
			c[0]='0';
			c[1]='\0';
			return c;
		}
	}
	else if(a[0]=='-' && b[0]=='-')//-a+b
	{
		if(len1<len2 || (len1==len2 && strcmp(a+1,b+1)<0))
			return sub_core(b+1,a+1);
		else if(len1>len2 || (len1==len2 && strcmp(a+1,b+1)>0))
		{
			c[0]='-';
			c[1]='\0';
			strcat(c,sub_core(a+1,b+1));
			return c;
		}
		else if(strcmp(a+1,b+1)==0)
		{
			c[0]='0';
			c[1]='\0';
			return c;
		}
	}
	else if(a[0]=='-' && b[0]!='-')//-a-b
	{
		c[0]='-';
		c[1]='\0';
		strcat(c,add_core(a+1,b));
		return c;
	}
	else if(a[0]!='-' && b[0]=='-')//a+b
	{
		return add_core(a,b+1);
	}
}
char* sub_core(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1>len2?len1:len2;
	char* c;
	int index1=len1-1,index2=len2-1,index=len-1;
	int temp,carry=0;
	c=(char*)malloc(sizeof(char)*(len+1));
	c[len]='\0';
	while(index1>=0 && index2>=0)
	{
		temp=(a[index1--]-'0')-(b[index2--]-'0')-carry;
		if(temp<0)
		{
			temp=10+temp;
			carry=1;
			c[index--]=temp+'0';
		}
		else
		{
			carry=0;
			c[index--]=temp+'0';
		}
	}
    while(index1>=0)
	{
		temp=(a[index1--]-'0')-carry;
		if(temp<0)
		{
			temp=10+temp;
			carry=1;
			c[index--]=temp+'0';
		}
		else
		{
			carry=0;
			c[index--]=temp+'0';
		}
	}
	index=0;
	while(c[index]=='0')
		index++;
	return c+index;

}
char* mul(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1+len2;
	char* c;
	c=(char*)malloc(sizeof(char)*(len+1));
	if(a[0]=='-' && b[0]=='-')
	{
		return mul_core(a+1,b+1);
	}
    if(a[0]=='-' && b[0]!='-')
	{
		c[0]='-';
		c[1]='\0';
		strcat(c,mul_core(a+1,b));
		return c;
	}
	if(a[0]!='-' && b[0]=='-')
	{
		c[0]='-';
		c[1]='\0';
		strcat(c,mul_core(a,b+1));
		return c;
	}
	if(a[0]!='-' && b[0]!='-')
	{
		return mul_core(a,b);
	}
}
char* mul_core(char* a,char* b)
{
    int len1=strlen(a);
	int len2=strlen(b);
	int len=len1+len2;
	char* c;
	int index1,index2,index;
	int temp,carry=0;
	
	c=(char*)malloc(sizeof(char)*(len+1));
	c[len]='\0';
	for(index=0;index<len;index++)
		c[index]='0';
	for(index2=len2-1;index2>=0;index2--)
	{
		for(index1=len1-1;index1>=0;index1--)
		{
			c[index1+index2+1]=(a[index1]-'0')*(b[index2]-'0')+c[index1+index2+1];
		}
	}
	for(index=len-1;index>=0;index--)
	{
		temp=c[index]-'0'+carry;
		if(temp>=10)
		{
			carry=temp/10;
			c[index]=temp%10+'0';
		}
		else
		{
			carry=0;
			c[index]=temp+'0';
		}
	}
	index=0;
	while(c[index]=='0')
		index++;
	if(index==len)
		return c+index-1;
	return c+index;
}
char* div(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1-len2+2>2?len1-len2+2:2;
	char* c;
	char* temp1;
	char* temp2;
	c=(char*)malloc(sizeof(char)*(len+1));
	temp1=a;
	temp2=b;
	if(a[0]=='-')
		temp1=a+1;
	if(b[0]=='-')
		temp2=b+1;

    c[0]='0';
	c[1]='\0';
	if(strlen(temp1)<strlen(temp2) || (strlen(temp1)==strlen(temp2) && strcmp(temp1,temp2)<0))
		return c;
    if(strcmp(b,c)==0)
		return NULL;

	if(a[0]=='-' && b[0]=='-')
		return div_core(a+1,b+1);
	if(a[0]=='-' && b[0]!='-')
	{
		c[0]='-';
		c[1]='\0';
		strcat(c,div_core(a+1,b));
		return c;
	}
	if(a[0]!='-' && b[0]=='-')
	{
		c[0]='-';
		c[1]='\0';
		strcat(c,div_core(a,b+1));
		return c;
	}
	if(a[0]!='-' && b[0]!='-')
	{
		return div_core(a,b);
	}
}
char* div_core(char* a,char* b)
{
	int len1=strlen(a);
	int len2=strlen(b);
	int len=len1-len2+2;
	int div_len=0;

	int index1=0;
	int index=0;
	char* c;
	char* div;
	char* pc;
	c=(char*)malloc(sizeof(char)*(len+1));
	div=(char*)malloc(sizeof(char)*(len2+2));
	pc=(char*)malloc(sizeof(char)*(len2+1));
	//div="";
    for(index=0;index<len;index++)
		c[index]='0';
	index=0;
	while(index1<len1)
	{
		while(div_len<len2 || (div_len==len2 && strcmp(div,b)<0))
		{
			//div_len=strlen(div);
			div[div_len]=a[index1++];
			div[div_len+1]='\0';
			div_len=strlen(div);
		}
		while(1)
		{
			pc=sub_core(div,b);
			if(strlen(pc)>len2 || (strlen(pc)==len2 && strcmp(pc,b)>0))
			    c[index]++;
			
			else 
				break;	
			strcpy(div,pc);
		}
		c[index]++;
		index++;
		
	}
	c[index]='\0';
	return c;
}