bal.cpp:2:6: warning: ISO C++ forbids declaration of 'main' with no type [-Wreturn-type]
main(){int n;std::stack<std::pair<double,double>>s;scanf("%d",&n);while(n--){double x,r;scanf("%lf %lf",&x,&r);while(s.size()){r=std::min(r,(x-s.top().first)*(x-s.top().first)/s.top().second/4);if(r>s.top().second)s.pop();else break;}s.push({x,r});printf("%.3f\n",r);}}
^
bal.cpp: In function 'int main()':
bal.cpp:2:57: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
main(){int n;std::stack<std::pair<double,double>>s;scanf("%d",&n);while(n--){double x,r;scanf("%lf %lf",&x,&r);while(s.size()){r=std::min(r,(x-s.top().first)*(x-s.top().first)/s.top().second/4);if(r>s.top().second)s.pop();else break;}s.push({x,r});printf("%.3f\n",r);}}
~~~~~^~~~~~~~~
bal.cpp:2:94: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
main(){int n;std::stack<std::pair<double,double>>s;scanf("%d",&n);while(n--){double x,r;scanf("%lf %lf",&x,&r);while(s.size()){r=std::min(r,(x-s.top().first)*(x-s.top().first)/s.top().second/4);if(r>s.top().second)s.pop();else break;}s.push({x,r});printf("%.3f\n",r);}}
~~~~~^~~~~~~~~~~~~~~~~