给定 2 个正整数 a, b，a 和 b 最多可能有 40 位，求出 a + b 的和(C语言实现)

#include <iostream>
#include <stdlib.h> 
#include <string.h>
using namespace std;
char * addChar(char *add1,char *add2,char *sum,int * carry);
int main()
{	 
	 char num[40] = {} ; 
	 
	 char num2[40] = {} ;
	 
	 char sum[40] = {} ; 
	 
	 cin >> num ;
	 cin >> num2 ;
	 
	 
	 //数字进行对齐
	 if(strlen(num) == strlen(num2))
	 {
	 	int carry = 0;
	 	addChar(num,num2,num,&carry);
	 	cout << num;
	 	return 0;
	 }
	 
	 if(strlen(num) > strlen(num2)) 
	 {
	 	//num大 
	 	int sub = strlen(num)-strlen(num2);
		int carry = 0;
		char *p = num + sub;
		addChar(num2,p,p,&carry);
		cout << num << endl;
		
	 }
	 else
	 {
	 	int sub = strlen(num2)-strlen(num);
		int carry = 0;
		char *p = num2 + sub;
		addChar(num,p,p,&carry);
		cout << num2 << endl;
	 } 	
} 
//相加 
char * addChar(char *add1,char *add2,char *sum,int * carry)
{
	if(strlen(add1) == strlen(add2))
	{
		for(int i = strlen(add1) - 1;i>=0;i--)
		{
			//48-57
			sum[i] = add1[i] + add2[i] - 48 + *carry;
			if(sum[i] > 57)
			{
				sum[i] -= 10;
				*carry = 1;
			}
			else
			{
				*carry = 0;
			}
			 
		}
		return sum;
	} 
	else
	{
		cout << "erro ,无法相加"<<endl;
		return NULL; 
	} 
	
}