Language: C++

#include<bits/stdc++.h>
using namespace std ;
	#define fastio ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
	#define lli long long int
	#define ulli unsigned long long int
	#define ff first
	#define ss second
	#define mp make_pair
	#define pb push_back
	#define pf pop_front()
	#define lb lower_bound
	#define ub upper_bound
	#define bs binary_search
	#define rep(i,a,b) for(lli i=a;i<b;i++)
	#define repe(i,a,b) for(lli i=a;i<=b;i++)
	#define all(v) v.begin(), v.end()
	#define mod 1000000007
	#define inf 100000000000000000
	#define lld long double
	#define pll pair<long long int,long long int>
	#define pii pair<int,int>
	#define vll vector<lli>
	#define vii vector<int>
	#define endl '\n'
	#define pie  acosl(-1.0);
	#define setp(k, x) fixed << setprecision(k) << (x)
	#define deb(x) cerr << #x << ": " << x << " " << endl;
	#define debug(x) cout << "m here-" <<#x<<" ..."<<"\n";
	#define printa(a,n) for(lli i=0;i<n;i++) cout<<a[i]<<" "; cout<<"\n";
  #define printv(a) for(lli i=0;i<a.size();i++) cout<<a[i]<<" "; cout<<"\n";
	bool sortcol( const vector<lli>& v1, const vector<lli>& v2 ) //sort on basis of column //use- sort(vect.begin(), vect.end(),sortcol);
      { return v1[1] < v2[1]; }//[] o based indexing in column
	bool sortpair(const pair<lli, lli> &a, const pair<lli, lli> &b)
			{return a.second < b.second;}
	struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        // http://xorshift.di.unimi.it/splitmix64.c
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>

//////////////////////////////////////////////////////////////////////////////////////////////
void solve();

//////////////////////////////////////////////////////////////////////////////////////////////
  int  dp[c+1][d+1];
int main ()
{
	// fastio
 	// lli  t;
 	// cin>>t;
 	// while(t--)
 	{
	solve();

 	}
}
///////////////////////////////////////////
void solve()
{
	lli n,i,d,a,b,c,j,k;
  string s1,s2,s3;
  cin>>s1>>s2;


  c= s1.length();
  d= s2.length();

  // a= lcs(s1,s2,c,d);
  // deb(a)
  // reverse(all(s3));
  // deb(s3)

  // debug(234)


  memset(dp,0,sizeof(dp));

  // debug(12)
  for(i=0;i<c+1;i++)
  {
    dp[i][0]=0;
  }

  for(i=0;i<d+1;i++)
  {
    dp[0][i]=0;
  }
  // debug(1)

  for(i=1;i<c+1;i++)
  {
    for(j=1;j<d+1;j++)
    {
      if(s1[i-1]==s2[j-1])
        dp[i][j]= (1+dp[i-1][j-1]);
      else
        dp[i][j]= max(dp[i][j-1], dp[i-1][j]);
    }
  }
  //
  // for(i=0;i<c+1;i++)
  // {
  //   for(j=0;j<d+1;j++){
  //     cout<<dp[i][j]<<" ";
  //
  //   }
  //   cout<<"\n";
  // }
  // //
  i= c;
  j= d;
  while(i>0 or j>0)
  {
    if(s1[i-1]==s2[j-1])
      {
        s3+=s1[i-1];
        i--;
        j--;
      }
    else
        {
          if(dp[i-1][j]<dp[i][j-1])
          {
            j--;
          }
          else
            i--;


        }

  }
  reverse(all(s3));
  cout<<s3<<"\n";





}


Compiler output:
a.cc:59:11: error: 'c' was not declared in this scope
   59 |   int  dp[c+1][d+1];
      |           ^
a.cc:59:16: error: 'd' was not declared in this scope
   59 |   int  dp[c+1][d+1];
      |                ^
a.cc: In function 'void solve()':
a.cc:90:10: error: 'dp' was not declared in this scope; did you mean 'd'?
   90 |   memset(dp,0,sizeof(dp));
      |          ^~
      |          d