Language: C++

#include <iostream>
#include <iomanip>
#include <vector>
#include <set>
#include <map>
#include <list>
#include <iterator>
#include <queue>
#include <stack>
#include <deque>
#include <sstream>
#include <algorithm>
#include <numeric>
#include <string>
#include <cmath>
#include <complex>
#include <functional>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cassert>
#include <cstdlib>
#include <cctype>

#define REP(i,m,n) for(int i=m;i<(int)n;i++)
#define rep(i,n) for(int i=0;i<(int)n;i++)
#define rrep(i,n) for(int i = 1; i <= n; i++)
#define drep(i,n) for(int i = n; i >= 0; i--)
#define rp(i,c) rep(i,(int)c.size())
#define fr(i,c) for(__typeof((c).begin()) i=(c).begin();i!=(c).end();i++)
#define mp make_pair
#define pb push_back
#define all(c) (c).begin(),(c).end()
#define rall(u) (u).rbegin(),(u).rend()
#define dbg(x) cerr<<#x<<" = "<<(x)<<endl
#define v_delete(a,b) (a).erase(remove((a).begin(), (a).end(), b), (a).end())
#define v_unique(a) (a).erase(unique((a).begin(), (a).end()), (a).end())
#define VV(T) vector<vector< T > >
#define init(a,b) memset((a), (b), sizeof((a)))
using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pii;
const int inf=1<<28;
const double INF=1e10,EPS=1e-9;


template<class T>int SIZE(T a){return a.size();}
template<class T>string IntToString(T num){string res;stringstream ss;ss<<num;return ss.str();}
template<class T>T StringToInt(string str){T res=0;for(int i=0;i<SIZE(str);i++)res=(res*10+str[i]-'0');return res;}
template<class T>T gcd(T a,T b){if(b==0)return a;return gcd(b,a%b);}
template<class T>T lcm(T a,T b){return a/gcd(a,b)*b;}

template <class T> void input(T& a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }
template <class T> void input(T* a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }


int dp[4002][4002]={0};
int main(){
	string a,b;
	while(cin >> a,a!=EOF){
	int as=a.size();
	a+='a';
	int bs=b.size();
	b+='b';
	int ans=0;
	for(int i=0;i<as;i++){
		for(int j=0;j<bs;j++){
			if(a[i+1]==b[j+1]){
				dp[i+1][j+1]=dp[i][j]+1;
			}else{
				dp[i+1][j+1]=0;
			}/*
			if(dp[i+1][j+1]){
				cout << dp[i+1][j+1]<<endl;
				cout << i << "," << j << endl;
			}*/
			ans=max(ans,dp[i+1][j+1]);
		}
	}
	cout << ans << endl;
	}
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:62:25: error: no match for 'operator!=' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'int')
   62 |         while(cin >> a,a!=EOF){
      |                        ~^~
      |                        |
      |                        std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/iosfwd:42,
                 from /usr/include/c++/14/ios:40,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/postypes.h:197:5: note: candidate: 'template<class _StateT> bool std::operator!=(const fpos<_StateT>&, const fpos<_StateT>&)'
  197 |     operator!=(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:197:5: note:   template argument deduction/substitution failed:
In file included from /usr/include/c++/14/cstdio:42,
                 from /usr/include/c++/14/ext/string_conversions.h:45,
                 from /usr/include/c++/14/bits/basic_string.h:4154,
                 from /usr/include/c++/14/string:54,
                 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:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::fpos<_StateT>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:243:5: note: candidate: 'template<class _T1, class _T2> bool std::operator!=(const allocator<_CharT>&, const allocator<_T2>&)'
  243 |     operator!=(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:243:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::allocator<_CharT>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
In file included from /usr/include/c++/14/string:48:
/usr/include/c++/14/bits/stl_iterator.h:455:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  455 |     operator!=(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:455:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  500 |     operator!=(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:500:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1686 |     operator!=(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1686:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator!=(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1753 |     operator!=(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1753:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51:
/usr/include/c++/14/bits/stl_pair.h:1052:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator!=(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1052 |     operator!=(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1052:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::pair<_T1, _T2>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
In file included from /usr/include/c++/14/bits/basic_string.h:47:
/usr/include/c++/14/string_view:651:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  651 |     operator!=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:651:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::__cxx11::basic_string<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/string_view:658:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  658 |     operator!=(basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:658:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::__cxx11::basic_string<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/string_view:666:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator!=(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  666 |     operator!=(__type_identity_t<basic_string_view<_CharT, _Traits>> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:666:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   mismatched types 'std::basic_string_view<_CharT, _Traits>' and 'int'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/bits/basic_string.h:3833:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3833 |     operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3833:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   mismatched types 'const std::__cxx11::basic_string<_CharT, _Traits, _Allocator>' and 'int'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/bits/basic_string.h:3847:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const _CharT*, const __cxx11::basic_string<_CharT, _Traits, _Allocator>&)'
 3847 |     operator!=(const _CharT* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3847:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   mismatched types 'const _CharT*' and 'std::__cxx11::basic_string<char>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
/usr/include/c++/14/bits/basic_string.h:3860:5: note: candidate: 'template<class _CharT, class _Traits, class _Alloc> bool std::operator!=(const __cxx11::basic_string<_CharT, _Traits, _Allocator>&, const _CharT*)'
 3860 |     operator!=(const basic_string<_CharT, _Traits, _Alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/basic_string.h:3860:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   mismatched types 'const _CharT*' and 'int'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
In file included from /usr/include/c++/14/bits/memory_resource.h:47,
                 from /usr/include/c++/14/string:68:
/usr/include/c++/14/tuple:2613:5: note: candidate: 'template<class ... _TElements, class ... _UElements> constexpr bool std::operator!=(const tuple<_UTypes ...>&, const tuple<_Elements ...>&)'
 2613 |     operator!=(const tuple<_TElements...>& __t,
      |     ^~~~~~~~
/usr/include/c++/14/tuple:2613:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::tuple<_UTypes ...>'
   62 |         while(cin >> a,a!=EOF){
      |                           ^~~
In file included from /usr/include/c++/14/bits/locale_facets.h:48,
                 from /usr/include/c++/14/bits/basic_ios.h:37,
                 from /usr/include/c++/14/ios:46:
/usr/include/c++/14/bits/streambuf_iterator.h:242:5: note: candidate: 'template<class _CharT, class _Traits> bool std::operator!=(const istreambuf_iterator<_CharT, _Traits>&, const istreambuf_iterator<_CharT, _Traits>&)'
  242 |     operator!=(const istreambuf_iterator<_CharT, _Traits>& __a,
      |     ^~~~~~~~
/usr/include/c++/14/bits/streambuf_iterator.h:242:5: note:   template argument deduction/substitution failed:
a.cc:62:27: note:   'std::string