Language: C++

#include <bits/stdc++.h>
using namespace std;
 
//DEFINE and TYPEDEF--------------------------------------------------------------
// For actual content check from line 100
#define timeKyaHorhaH 1.0 * clock() / CLOCKS_PER_SEC

#define FORG(i,a,n) for(lld i=(lld)a;a<n?i<(lld)n:(lld)n<i;a<n?++i:--i) //for - general
#define FORZ(i,n) for(lld i=0;i<(lld)n;++i) //for - zero
#define FORGI(i,a,n,inc) for(lld i=(lld)a;a<n?i<(lld)n:(lld)n<i;a<n?i+=inc:i-=inc) //for - general incremental
#define FORZI(i,n,inc) for(lld i=0;i<(lld)n;i+=inc) //for - zero incremental
#define SPEEDUP ios_base::sync_with_stdio(0); cin.tie(NULL); cout.tie(NULL);
#define MEM(a,val) memset(a,val,sizeof(a));
 
#define SORTall(m) sort(m.begin(),m.end());
#define all(m) m.begin(),m.end()
 
#define st first
#define nd second
#define pb push_back
#define DEC(x) fixed<<setprecision(x)
 
typedef long long int lld;
typedef unsigned long long int ulld;
 
//DEBUGGER------------------------------------------------------------------------
// #define DEBUG(x) cerr<<(#x)<<" is "<<(x)<<"\n" //to debug values of variables
#define DEBUGON
#define ZINDA cerr<<"\nIdhar-ich hai apun!!\n"; //to debug if code reached that point

#ifdef DEBUGON
	vector<string> vec_splitter(string s) 
	{
		for(char& c: s) c = c == ',' ?  ' ': c;
		stringstream ss; ss << s;
		vector<string> res;
		for(string z; ss >> z; res.push_back(z));
		return res;
	}

	void debug_out(vector<string> args, int idx) { cerr << endl; }
	template <typename Head, typename... Tail>
		void debug_out(vector<string> args, int idx, Head H, Tail... T) 
		{
			if(idx > 0) cerr << ", ";
			stringstream ss; ss << H;
			cerr << args[idx] << " = " << ss.str();
			debug_out(args, idx + 1, T...);
		}

	#define debug(...) debug_out(vec_splitter(#__VA_ARGS__), 0, __VA_ARGS__);
	#define DEBUG(...) debug_out(vec_splitter(#__VA_ARGS__), 0, __VA_ARGS__);	
#else
	#define debug(...) 320;
	#define DEBUG(...) 320;
#endif

lld power(lld b, lld e)
{
	assert(e>=0);
    if(e==0)
        return 1;
    if(e%2==1)
        return b*power(b*b,(e-1)/2);
    else
        return power(b*b,e/2);
}
 
lld power(lld b, lld e, lld m)
{
	assert(e>=0);
	if(e==0)
		return 1;
	if(e%2==1)
		return b*power(((b%m)*(b%m))%m,(e-1)/2,m)%m;
	else
		return power(((b%m)*(b%m))%m,e/2,m)%m;
}
 
int nDig(lld n)
{
	if(n<0) 
		n*=-1;
	if(n==0)
		return 1;

    return floor(log10(n) + 1);
}

int lognk(lld n, lld k) // logk(n)
{
	assert(n>=0 and k>=0 and k!=1);
	if(n==0)
		return -1;

	return lognk(n/k,k)+1;
}

const long double pi = acos(-1);
#define endl '\n'
#define mod 1000000007

//endl : changed to '\n', to flush comment that definition
//--------------------------------------------------------------------------------

void swagWaalaFunction()
{
	lld n,ans=0;
	cin>>n;

	ans=power(a,2)+power(a,3)+a;
	cout<<ans;
	return;
}

int main()
{
    SPEEDUP;
 	lld t=1;
 	//cin>>t;

 	#ifdef PRIMES
 		sieve();
 	#endif

 	#ifdef CHOOSE
 		nCrModInit();
 	#endif

 	while(t--)
 		swagWaalaFunction();
	
	// cerr<<"\n"<<timeKyaHorhaH; 	
 	return 0;
}

Compiler output:
a.cc: In function 'void swagWaalaFunction()':
a.cc:111:19: error: 'a' was not declared in this scope
  111 |         ans=power(a,2)+power(a,3)+a;
      |                   ^