Language: C++

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
int dp[101][4][4][4];
int mod=1e9+7;
int main(){
	int n;
	cin>>n;
	dp[0][3][3][3]=1;
	for(int len=0;len<n;len++)
	 
	 	for(int c1=0;c1<4;c1++)
	 	
	 		for(int c2=0;c2<4;c2++)
	 		
	 			for(int c3=0;c3<4;c3++)
	 			
	 				if(dp[len][c1][c2][c3]==0)continue;
	 				for(int a=0;a<4;a++)
	 				
	 					if(a==2&&c1==1&&c2==0)continue;
	 					if(a==2&&c1==0&&c2==1)continue;
	 					if(a==1&&c1==2&&c2==0)continue;
	 					if(a==2&&c1==1&&c3==0)continue;
	 					if(a==2&&c2==1&&c3==0)continue;
	 					dp[len+1][a][c1][c2]+=dp[len][c1][c2][c3];
						dp[len+1][a][c1][c2]%=mod;  
			
	 int ans=0;
	 for(int c1=0;c1<4;c1++)
	 
	 	for(int c2=0;c2<4;c2++)
	 	
	 		for(int c3=0;c3<4;c3++)
	 		
	 			ans+=dp[n][c1][c2][c3];
	 			ans%=mod;
	
	 cout<<ans<<endl;
} 

Compiler output:
a.cc: In function 'int main()':
a.cc:21:58: error: 'c1' was not declared in this scope; did you mean 'y1'?
   21 |                                                 if(a==2&&c1==1&&c2==0)continue;
      |                                                          ^~
      |                                                          y1
a.cc:21:65: error: 'c2' was not declared in this scope
   21 |                                                 if(a==2&&c1==1&&c2==0)continue;
      |                                                                 ^~
a.cc:22:52: error: 'a' was not declared in this scope
   22 |                                                 if(a==2&&c1==0&&c2==1)continue;
      |                                                    ^
a.cc:22:58: error: 'c1' was not declared in this scope; did you mean 'y1'?
   22 |                                                 if(a==2&&c1==0&&c2==1)continue;
      |                                                          ^~
      |                                                          y1
a.cc:22:65: error: 'c2' was not declared in this scope
   22 |                                                 if(a==2&&c1==0&&c2==1)continue;
      |                                                                 ^~
a.cc:22:71: error: continue statement not within a loop
   22 |                                                 if(a==2&&c1==0&&c2==1)continue;
      |                                                                       ^~~~~~~~
a.cc:23:52: error: 'a' was not declared in this scope
   23 |                                                 if(a==1&&c1==2&&c2==0)continue;
      |                                                    ^
a.cc:23:58: error: 'c1' was not declared in this scope; did you mean 'y1'?
   23 |                                                 if(a==1&&c1==2&&c2==0)continue;
      |                                                          ^~
      |                                                          y1
a.cc:23:65: error: 'c2' was not declared in this scope
   23 |                                                 if(a==1&&c1==2&&c2==0)continue;
      |                                                                 ^~
a.cc:23:71: error: continue statement not within a loop
   23 |                                                 if(a==1&&c1==2&&c2==0)continue;
      |                                                                       ^~~~~~~~
a.cc:24:52: error: 'a' was not declared in this scope
   24 |                                                 if(a==2&&c1==1&&c3==0)continue;
      |                                                    ^
a.cc:24:58: error: 'c1' was not declared in this scope; did you mean 'y1'?
   24 |                                                 if(a==2&&c1==1&&c3==0)continue;
      |                                                          ^~
      |                                                          y1
a.cc:24:65: error: 'c3' was not declared in this scope
   24 |                                                 if(a==2&&c1==1&&c3==0)continue;
      |                                                                 ^~
a.cc:24:71: error: continue statement not within a loop
   24 |                                                 if(a==2&&c1==1&&c3==0)continue;
      |                                                                       ^~~~~~~~
a.cc:25:52: error: 'a' was not declared in this scope
   25 |                                                 if(a==2&&c2==1&&c3==0)continue;
      |                                                    ^
a.cc:25:58: error: 'c2' was not declared in this scope
   25 |                                                 if(a==2&&c2==1&&c3==0)continue;
      |                                                          ^~
a.cc:25:65: error: 'c3' was not declared in this scope
   25 |                                                 if(a==2&&c2==1&&c3==0)continue;
      |                                                                 ^~
a.cc:25:71: error: continue statement not within a loop
   25 |                                                 if(a==2&&c2==1&&c3==0)continue;
      |                                                                       ^~~~~~~~
a.cc:26:52: error: 'len' was not declared in this scope
   26 |                                                 dp[len+1][a][c1][c2]+=dp[len][c1][c2][c3];
      |                                                    ^~~
a.cc:26:59: error: 'a' was not declared in this scope
   26 |                                                 dp[len+1][a][c1][c2]+=dp[len][c1][c2][c3];
      |                                                           ^
a.cc:26:62: error: 'c1' was not declared in this scope; did you mean 'y1'?
   26 |                                                 dp[len+1][a][c1][c2]+=dp[len][c1][c2][c3];
      |                                                              ^~
      |                                                              y1
a.cc:26:66: error: 'c2' was not declared in this scope
   26 |                                                 dp[len+1][a][c1][c2]+=dp[len][c1][c2][c3];
      |                                                                  ^~
a.cc:26:87: error: 'c3' was not declared in this scope
   26 |                                                 dp[len+1][a][c1][c2]+=dp[len][c1][c2][c3];
      |                                                                                       ^~