c++判断并求三角形面积

#include<bits/stdc++.h> using namespace std; int main() {  double a,b,c,p,s;  cin>>a>>b>>c;  if (a+b>c && a+c>b && b+c>a)  {   p=(a+b+c)/2;  s=sqrt(p*(p-a)*(p-b)*(p-c));  cout<<"s="<<s;  } else cout<<"can't"<<endl;  return 0; }