Language: C++

#include<bits/stdc++.h>
/************************************************/
#define rep(i,n) for(int i=0;i<n;i++)
#define mp make_pair
#define pb push_back
#define fr first
#define se second
#define forn(i,a,n) for(int i=a;i<n;i++)
#define foreach(i,c) for(__typeof(c.begin())i=(c.begin());i!=(c).end();i++)
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define sz(s) s.size()
#define all(s) s.begin(),s.end()
#define zero(x) memset(x,0,sizeof(x))
#define vii vector<pair<int,int> >
#define mpis map<int,string>
#define mpii map<int,int>
#define mpsi map<string,int>
#define re return
/************************************************/
int main(){
 	long double a,b,k;
 	cin>>a>>b>>k;
 	long double t=a*a*b;
	long double l=t-k;
	if(l<=t/2){
		long double h=l*2/(a*a);
    	long double tb=sqrt(h*h+a*a);
    	cout<<fixed<<setprecision(8)<<asin(h/tb)/M_PI*180<<endl;
  	}
	else{
	  	l=k;
	  	double h=l*2/(b*a);
	  	double tb=sqrt(h*h+b*b);
	  	cout<<fixed<<setprecision(8)<<90-asin(h/tb)/M_PI*180<<endl;
	}
	re 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:24:9: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
   24 |         cin>>a>>b>>k;
      |         ^~~
      |         std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:30:9: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   30 |         cout<<fixed<<setprecision(8)<<asin(h/tb)/M_PI*180<<endl;
      |         ^~~~
      |         std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:30:15: error: 'fixed' was not declared in this scope
   30 |         cout<<fixed<<setprecision(8)<<asin(h/tb)/M_PI*180<<endl;
      |               ^~~~~
a.cc:30:15: note: suggested alternatives:
In file included from /usr/include/c++/14/streambuf:43,
                 from /usr/include/c++/14/bits/streambuf_iterator.h:35,
                 from /usr/include/c++/14/iterator:66,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:54:
/usr/include/c++/14/bits/ios_base.h:1104:3: note:   'std::fixed'
 1104 |   fixed(ios_base& __base)
      |   ^~~~~
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:198:
/usr/include/c++/14/charconv:622:21: note:   'std::chars_format::fixed'
  622 |     scientific = 1, fixed = 2, hex = 4, general = fixed | scientific
      |                     ^~~~~
a.cc:30:22: error: 'setprecision' was not declared in this scope; did you mean 'std::setprecision'?
   30 |         cout<<fixed<<setprecision(8)<<asin(h/tb)/M_PI*180<<endl;
      |                      ^~~~~~~~~~~~
      |                      std::setprecision
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:143:
/usr/include/c++/14/iomanip:202:3: note: 'std::setprecision' declared here
  202 |   setprecision(int __n)
      |   ^~~~~~~~~~~~
a.cc:30:60: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   30 |         cout<<fixed<<setprecision(8)<<asin(h/tb)/M_PI*180<<endl;
      |                                                            ^~~~
      |                                                            std::endl
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:36:17: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   36 |                 cout<<fixed<<setprecision(8)<<90-asin(h/tb)/M_PI*180<<endl;
      |                 ^~~~
      |                 std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:36:23: error: 'fixed' was not declared in this scope
   36 |                 cout<<fixed<<setprecision(8)<<90-asin(h/tb)/M_PI*180<<endl;
      |                       ^~~~~
a.cc:36:23: note: suggested alternatives:
/usr/include/c++/14/bits/ios_base.h:1104:3: note:   'std::fixed'
 1104 |   fixed(ios_base& __base)
      |   ^~~~~
/usr/include/c++/14/charconv:622:21: note:   'std::chars_format::fixed'
  622 |     scientific = 1, fixed = 2, hex = 4, general = fixed | scientific
      |                     ^~~~~
a.cc:36:30: error: 'setprecision' was not declared in this scope; did you mean 'std::setprecision'?
   36 |                 cout<<fixed<<setprecision(8)<<90-asin(h/tb)/M_PI*180<<endl;
      |                              ^~~~~~~~~~~~
      |                              std::setprecision
/usr/include/c++/14/iomanip:202:3: note: 'std::setprecision' declared here
  202 |   setprecision(int __n)
      |   ^~~~~~~~~~~~
a.cc:36:71: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   36 |                 cout<<fixed<<setprecision(8)<<90-asin(h/tb)/M_PI*180<<endl;
      |                                                                       ^~~~
      |                                                                       std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~