View Compilation Error

0_0_37425286_32563.cpp: In function 'bool sushu(int, int)':
0_0_37425286_32563.cpp:9:25: error: 'sqrt' was not declared in this scope
  for(int i=2;i<=sqrt(ans);i++)
                         ^
0_0_37425286_32563.cpp: In function 'int dfs(int)':
0_0_37425286_32563.cpp:25:3: error: return-statement with no value, in function returning 'int' [-fpermissive]
   return ;
   ^
0_0_37425286_32563.cpp: In function 'int main()':
0_0_37425286_32563.cpp:46:3: error: expected ';' before 'dfs'
   dfs(1);
   ^