foo.cpp:3:5: error: cannot declare '::main' to be a global variable
 int main{
     ^~~~
foo.cpp:4:2: error: expected primary-expression before 'int'
  int k;
  ^~~
foo.cpp:4:2: error: expected '}' before 'int'
foo.cpp:6:2: error: expected unqualified-id before 'while'
  while(j<=k)
  ^~~~~
foo.cpp:12:2: error: 'cout' does not name a type
  cout<<i*i+j*j;
  ^~~~
foo.cpp:13:1: error: expected declaration before '}' token
 }
 ^