Language: C++

#include<iostream>
#include<stdio.h>
#include<ctype.h>
#include<string>
#include<cmath>
#include<math.h>
#include<vector>
#include<stdlib.h>
#include<algorithm>
#include<functional>

using namespace std;

#define OUT cout <<
#define IN cin >>
#define E << endl;
#define FOR(i,a,b) for(int i = a;i < b;i++)

char c[10];
int array[10];
int array2[10];

void input(){
	FOR(i, 0, 10){
		array[i] = c[i] - '0';
	}
}

int main(){
	while(IN c){
		input();
		for(int i = 9; i >= 0; i--){
			for(int j = 0; j <  i; j++){
				array2[j] = (array[j] + array[j + 1]) % 10;
	     	}
			for(int j = 0; j <  i; j++){
				array[j] = array2[j];
			}
		}	
		OUT array[0] E
	}

}

Compiler output:
a.cc: In function 'void input()':
a.cc:25:17: error: reference to 'array' is ambiguous
   25 |                 array[i] = c[i] - '0';
      |                 ^~~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_pair.h:99:12: note: candidates are: 'template<class _Tp, long unsigned int _Nm> struct std::array'
   99 |     struct array;
      |            ^~~~~
a.cc:20:5: note:                 'int array [10]'
   20 | int array[10];
      |     ^~~~~
a.cc: In function 'int main()':
a.cc:34:46: error: reference to 'array' is ambiguous
   34 |                                 array2[j] = (array[j] + array[j + 1]) % 10;
      |                                              ^~~~~
/usr/include/c++/14/bits/stl_pair.h:99:12: note: candidates are: 'template<class _Tp, long unsigned int _Nm> struct std::array'
   99 |     struct array;
      |            ^~~~~
a.cc:20:5: note:                 'int array [10]'
   20 | int array[10];
      |     ^~~~~
a.cc:34:57: error: reference to 'array' is ambiguous
   34 |                                 array2[j] = (array[j] + array[j + 1]) % 10;
      |                                                         ^~~~~
/usr/include/c++/14/bits/stl_pair.h:99:12: note: candidates are: 'template<class _Tp, long unsigned int _Nm> struct std::array'
   99 |     struct array;
      |            ^~~~~
a.cc:20:5: note:                 'int array [10]'
   20 | int array[10];
      |     ^~~~~
a.cc:37:33: error: reference to 'array' is ambiguous
   37 |                                 array[j] = array2[j];
      |                                 ^~~~~
/usr/include/c++/14/bits/stl_pair.h:99:12: note: candidates are: 'template<class _Tp, long unsigned int _Nm> struct std::array'
   99 |     struct array;
      |            ^~~~~
a.cc:20:5: note:                 'int array [10]'
   20 | int array[10];
      |     ^~~~~
a.cc:40:21: error: reference to 'array' is ambiguous
   40 |                 OUT array[0] E
      |                     ^~~~~
/usr/include/c++/14/bits/stl_pair.h:99:12: note: candidates are: 'template<class _Tp, long unsigned int _Nm> struct std::array'
   99 |     struct array;
      |            ^~~~~
a.cc:20:5: note:                 'int array [10]'
   20 | int array[10];
      |     ^~~~~