Language: C++

#define debug_interval ','
#define dump_interval ' '
#define debug_toggle 1
//{
#include<bits/stdc++.h>
using namespace std;
#define hi cerr<<"hi"<<endl;
#define int long long
#define INT_MAX LLONG_MAX
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define fi first
#define se second
#define mp make_pair
#define rev reverse
#define dans dump(ans)
#define MOD 1000000007
#define amp(v,n) (v).count(n)?v[n]++:v[n]=1
#define sysp system("pause")
#define PI acos(-1)
#define pf push_front
#define ins insert

//{
inline int toInt(string s){int v;istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x){ostringstream sout;sout<<x;return sout.str();}
template<class...A> inline void dump(){cout<<endl;}
template<class...A> inline void dump_rest() {cout<<endl;}
template<class T, class...A> inline void dump_rest(const T& first, const A&... rest){cout<<dump_interval<<first;dump_rest(rest...);}
template<class T,class...A> inline void dump(const T&first,const A&...rest){cout<<first;dump_rest(rest...);}
template<class...A> inline void debug(){cerr<<endl;}
template<class...A> inline void debug_rest() {cerr<<endl;}
template<class T, class...A> inline void debug_rest(const T& first, const A&... rest){cerr<<debug_interval<<first;debug_rest(rest...);}
template<class T,class...A> inline void debug(const T&first,const A&...rest){if(debug_toggle)cerr<<first,debug_rest(rest...);}
unsigned XorShift(void){static unsigned x = 123456789;static unsigned y = 362436069;static unsigned z = 521288629;static unsigned w = 88675123;unsigned t;t = x ^ (x << 11);x = y; y = z; z = w;return w = (w ^ (w >> 19)) ^ (t ^ (t >> 8));}
//}

typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;

template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}
template<int m>class mint{private:int i;public:mint() : i(0){}mint(int i): i((i%m+m)%m){}mint operator+(const mint& o){return o.i+i;}mint operator*(const mint& o){return o.i*i;}mint operator-(){return -i;}operator int() {return i;}};

//}

int ans;

main(){
    string s;
    cin>>s;
    int t=0;
    rep(i,s.size()){
        if(s[i]=='A')t++;
        else if(s[i]=='T')t++;
        else if(s[i]=='G')t++;
        else if(s[i]=='C')t++;
        else{
            chmax(ans,t);
            t=0;
        }
    }
    rev(all(s));
    int t=0;
    rep(i,s.size()){
        if(s[i]=='A')t++;
        else if(s[i]=='T')t++;
        else if(s[i]=='G')t++;
        else if(s[i]=='C')t++;
        else{
            chmax(ans,t);
            t=0;
        }
    }
    dans;
}





Compiler output:
a.cc:9:9: warning: "INT_MAX" redefined
    9 | #define INT_MAX LLONG_MAX
      |         ^~~~~~~
In file included from /usr/include/c++/14/climits:42,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:38,
                 from a.cc:5:
/usr/lib/gcc/x86_64-linux-gnu/14/include/limits.h:120:9: note: this is the location of the previous definition
  120 | #define INT_MAX __INT_MAX__
      |         ^~~~~~~
a.cc:53:1: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
   53 | main(){
      | ^~~~
a.cc: In function 'int main()':
a.cc:68:9: error: redeclaration of 'long long int t'
   68 |     int t=0;
      |         ^
a.cc:56:9: note: 'long long int t' previously declared here
   56 |     int t=0;
      |         ^