Language: C++

#include <cstdio>
#include <cstring>
#include <algorithm>

#define MAX_SIZE 90;

#define toI(x) (x-'0')

using namespace std;

class Z
{
private:
  int size;
  char d[MAX_SIZE];
public:
  Z(char *s)
  {
    size = strlen(s);
    for(int i=0;i<MAX_SIZE - size;i++)
      d[i] = 0;
    for(int i=0,j=MAX_SIZE - size;j < MAX_SIZE; i++, j++)
      d[j] = s[i];
  }

  void add(Z r)
  {
    int tmp = max(this->size, r.size);
    int updigit = 0;
    for(int i=MAX_SIZE-1;i>=0;i--){
      int a = 0, b = 0;
      if(this->d[i] == 0&& r.d[i] == 0){
	if(!updigit)
	  goto end;
	this->d[i] = updigit+'0';
	updigit = 0;
	tmp++;
      }else{
	if(this->d[i])
	  a = toI(this->d[i]);
	if(r.d[i])
	  b = toI(r.d[i]);
	int n = a + b + updigit;
	updigit = n / 10;
	this->d[i] = (n % 10)+'0';
      }
    }
  end:
    this->size = tmp;
    return;
  }

  void print()
  {
    if(this->size > 80){
      puts("overflow");
      return;
    }
    for(int i=0;i<MAX_SIZE;i++)
      if(d[i] != -1)
	putchar(d[i]);
    puts("");
  }

  int sz()
  {
    return this->size;
  }
};

int main()
{
  int x;
  scanf("%d", &x);
  char s1[MAX_SIZE], s2[MAX_SIZE];  
  for(int i=0;i<x;i++){
 /*   scanf("%s%s",s1, s2);
   Z z1(s1);
    Z z2(s2);
    if(z1.sz() > 80 || z2.sz() > 80){
      puts("overflow");
      continue;
    }
    z1.add(z2);
    z1.print(); */
  }
  return 0;
}

Compiler output:
a.cc:5:20: error: expected ']' before ';' token
    5 | #define MAX_SIZE 90;
      |                    ^
a.cc:15:10: note: in expansion of macro 'MAX_SIZE'
   15 |   char d[MAX_SIZE];
      |          ^~~~~~~~
a.cc:15:18: error: expected unqualified-id before ']' token
   15 |   char d[MAX_SIZE];
      |                  ^
a.cc: In constructor 'Z::Z(char*)':
a.cc:20:34: error: expected ')' before ';' token
   20 |     for(int i=0;i<MAX_SIZE - size;i++)
      |                                  ^
a.cc:20:8: note: to match this '('
   20 |     for(int i=0;i<MAX_SIZE - size;i++)
      |        ^
a.cc:20:35: error: 'i' was not declared in this scope
   20 |     for(int i=0;i<MAX_SIZE - size;i++)
      |                                   ^
a.cc:5:20: error: expected ')' before ';' token
    5 | #define MAX_SIZE 90;
      |                    ^
a.cc:22:39: note: in expansion of macro 'MAX_SIZE'
   22 |     for(int i=0,j=MAX_SIZE - size;j < MAX_SIZE; i++, j++)
      |                                       ^~~~~~~~
a.cc:22:8: note: to match this '('
   22 |     for(int i=0,j=MAX_SIZE - size;j < MAX_SIZE; i++, j++)
      |        ^
a.cc:22:54: error: 'j' was not declared in this scope
   22 |     for(int i=0,j=MAX_SIZE - size;j < MAX_SIZE; i++, j++)
      |                                                      ^
a.cc: In member function 'void Z::add(Z)':
a.cc:30:30: error: expected ')' before ';' token
   30 |     for(int i=MAX_SIZE-1;i>=0;i--){
      |                              ^
a.cc:30:8: note: to match this '('
   30 |     for(int i=MAX_SIZE-1;i>=0;i--){
      |        ^
a.cc:30:31: error: 'i' was not declared in this scope
   30 |     for(int i=MAX_SIZE-1;i>=0;i--){
      |                               ^
a.cc: In member function 'void Z::print()':
a.cc:59:27: error: expected primary-expression before ';' token
   59 |     for(int i=0;i<MAX_SIZE;i++)
      |                           ^
a.cc:59:27: error: expected ')' before ';' token
a.cc:59:8: note: to match this '('
   59 |     for(int i=0;i<MAX_SIZE;i++)
      |        ^
a.cc:59:28: error: 'i' was not declared in this scope
   59 |     for(int i=0;i<MAX_SIZE;i++)
      |                            ^
a.cc: In function 'int main()':
a.cc:5:20: error: expected ']' before ';' token
    5 | #define MAX_SIZE 90;
      |                    ^
a.cc:75:11: note: in expansion of macro 'MAX_SIZE'
   75 |   char s1[MAX_SIZE], s2[MAX_SIZE];
      |           ^~~~~~~~
a.cc:75:19: error: expected primary-expression before ']' token
   75 |   char s1[MAX_SIZE], s2[MAX_SIZE];
      |                   ^
a.cc:75:33: error: expected primary-expression before ']' token
   75 |   char s1[MAX_SIZE], s2[MAX_SIZE];
      |                                 ^